A Zimbabwean Riot policeman looks at the campaign poster of main opposition leader, Nelson Chamisa outside the party headquarters in Harare, Zimbabwe, Thursday, Aug, 2, 2018. Zimbabwe's acting President said Thursday that his government had been in touch with the main opposition leader in an attempt to ease tensions after election related violence in the capital. (AP Photo/Tsvangirayi Mukwazhi)
PHOTO: Tsvangirayi Mukwazhi/AP
A Zimbabwean Riot policeman looks at the campaign poster of main opposition leader, Nelson Chamisa outside the party headquarters in Harare, Zimbabwe, Thursday, Aug, 2, 2018. Zimbabwe's acting President said Thursday that his government had been in touch with the main opposition leader in an attempt to ease tensions after election related violence in the capital. (AP Photo/Tsvangirayi Mukwazhi)
Now playing
01:28
Mnangagwa gets 51%, avoids runoff election
emmerson mnangagwa robert mugabe zimbabwe pkg curnow cnni_00003505.jpg
PHOTO: AFP/Getty Images
emmerson mnangagwa robert mugabe zimbabwe pkg curnow cnni_00003505.jpg
Now playing
02:14
ZImbabwe's Mnangagwa secures election victory
PHOTO: CNN PHOTO ILLUSTRATION/GETTY IMAGES
Now playing
02:53
Zimbabweans vote in first Mugabe-free election
Marketplace Africa Zimbabwe microbrewery a_00001612.jpg
Marketplace Africa Zimbabwe microbrewery a_00001612.jpg
Now playing
05:49
A taste of Zimbabwe's economic future
African Voices Zimbabwe dance hall winky d jamaica b_00000321.jpg
African Voices Zimbabwe dance hall winky d jamaica b_00000321.jpg
Now playing
07:03
Zimbabwe's biggest modern dance hall star
PHOTO: The Herald
Now playing
01:38
Explosion at presidential rally in Zimbabwe
PHOTO: Getty Images
Now playing
01:26
Zimbabwe's Mnangagwa sworn in as President
emmerson mnangagwa robert mugabe zimbabwe pkg curnow cnni_00003505.jpg
PHOTO: AFP/Getty Images
emmerson mnangagwa robert mugabe zimbabwe pkg curnow cnni_00003505.jpg
Now playing
01:25
Who is Emmerson Mnangagwa?
Protesters calling for the impeachment of President Robert Mugabe demonstrate outside the parliament building in downtown Harare, Zimbabwe Tuesday, Nov. 21, 2017. (AP Photo/Ben Curtis)
PHOTO: Ben Curtis/AP
Protesters calling for the impeachment of President Robert Mugabe demonstrate outside the parliament building in downtown Harare, Zimbabwe Tuesday, Nov. 21, 2017. (AP Photo/Ben Curtis)
Now playing
01:51
Celebration on Harare streets as Mugabe resigns
epa06342344 People celebrate outside parliament after hearing the news that President Robert Mugabe resigned in Harare, Zimbabwe, 21 November 2017. Zimbabwe's parliamentary speaker on 21 November said Mugabe has resigned as President via a letter to parliament after having been president of Zimbabwe for 37 years. This comes days after tens of thousands of people took to the streets of the capital to call for President Mugabe to step down.  EPA-EFE/KIM LUDBROOK
PHOTO: KIM LUDBROOK/EPA-EFE
epa06342344 People celebrate outside parliament after hearing the news that President Robert Mugabe resigned in Harare, Zimbabwe, 21 November 2017. Zimbabwe's parliamentary speaker on 21 November said Mugabe has resigned as President via a letter to parliament after having been president of Zimbabwe for 37 years. This comes days after tens of thousands of people took to the streets of the capital to call for President Mugabe to step down. EPA-EFE/KIM LUDBROOK
Now playing
00:49
Zimbabweans: Resignation is the work of God
Zimbabweans gather to pray for the country in a park opposite the parliament building in downtown Harare, Zimbabwe Tuesday, Nov. 21, 2017. Zimbabwean President Robert Mugabe should acknowledge the nation's "insatiable desire" for a leadership change and resign immediately, the recently fired vice president and likely successor to the 93-year-old leader said Tuesday. (AP Photo/Ben Curtis)
PHOTO: Ben Curtis/AP
Zimbabweans gather to pray for the country in a park opposite the parliament building in downtown Harare, Zimbabwe Tuesday, Nov. 21, 2017. Zimbabwean President Robert Mugabe should acknowledge the nation's "insatiable desire" for a leadership change and resign immediately, the recently fired vice president and likely successor to the 93-year-old leader said Tuesday. (AP Photo/Ben Curtis)
Now playing
02:11
Unrest grows outside Zimbabwe parliament
HARARE, ZIMBABWE:  Zimbabwean President Robert Mugabe clenches his fist to salute Zanu PF comrades in Harare, 03 May 2000. Mugabe launched his ruling party election manifesto today ahead the upcoming elections. (ELECTRONIC IMAGE) AFP PHOTO  ODD ANDERSEN. (Photo credit should read ODD ANDERSEN/AFP/Getty Images)
PHOTO: ODD ANDERSEN/AFP/AFP/Getty Images
HARARE, ZIMBABWE: Zimbabwean President Robert Mugabe clenches his fist to salute Zanu PF comrades in Harare, 03 May 2000. Mugabe launched his ruling party election manifesto today ahead the upcoming elections. (ELECTRONIC IMAGE) AFP PHOTO ODD ANDERSEN. (Photo credit should read ODD ANDERSEN/AFP/Getty Images)
Now playing
01:58
Robert Mugabe: What you need to know
Zimbabwe's President Robert Mugabe delivers a speech during the Zimbabwe ruling party Zimbabwe African National Union- Patriotic Front (Zanu PF) youth interface Rally on November 4, 2017 in Bulawayo. / AFP PHOTO / ZINYANGE AUNTONY        (Photo credit should read ZINYANGE AUNTONY/AFP/Getty Images)
PHOTO: ZINYANGE AUNTONY/AFP/Getty Images
Zimbabwe's President Robert Mugabe delivers a speech during the Zimbabwe ruling party Zimbabwe African National Union- Patriotic Front (Zanu PF) youth interface Rally on November 4, 2017 in Bulawayo. / AFP PHOTO / ZINYANGE AUNTONY (Photo credit should read ZINYANGE AUNTONY/AFP/Getty Images)
Now playing
01:20
Source: Mugabe agrees to resignation
Monitoring for coverage of coup.
PHOTO: Zimbabwe Broadcasting Corporation
Monitoring for coverage of coup.
Now playing
01:16
Zimbabwe's Mugabe refuses to resign
A man holding a flag of Zimbabwe takes part in a demonstration of University of Zimbabwe's students, on November 20, 2017 in Harare, to demand the withdrawal of Grace Mugabe's doctorate and refused to sit their exams as pressure builds on Zimbabwe's President Robert Mugabe to resign.
Zimbabwe's President faced the threat of impeachment by his own party on November 20, 2017, after his shock insistence he still holds power in Zimbabwe despite a military takeover and a noon deadline to end his 37-year autocratic rule.
 / AFP PHOTO / -        (Photo credit should read -/AFP/Getty Images)
PHOTO: AFP/Getty Images
A man holding a flag of Zimbabwe takes part in a demonstration of University of Zimbabwe's students, on November 20, 2017 in Harare, to demand the withdrawal of Grace Mugabe's doctorate and refused to sit their exams as pressure builds on Zimbabwe's President Robert Mugabe to resign. Zimbabwe's President faced the threat of impeachment by his own party on November 20, 2017, after his shock insistence he still holds power in Zimbabwe despite a military takeover and a noon deadline to end his 37-year autocratic rule. / AFP PHOTO / - (Photo credit should read -/AFP/Getty Images)
Now playing
02:17
Mugabe's prolonged exit fraying nerves
FILE - In this April 7,  2016 file photo Zimbabwean President Robert Mugabe attends a meeting with the country's war veterans in Harare.  Mugabe seemed almost untouchable for much of his nearly four-decade rule. Shrewd and ruthless, he managed to stay in power despite advancing age, growing opposition, international sanctions and the dissolving economy of a once-prosperous African nation. Now, the apparent abrupt end of the Mugabe era is launching Zimbabwe into the unknown. It's a humbling close to the career of a man who crushed dissent or sidelined opponents after leading Zimbabwe since 1980. (AP Photo/Tsvangirayi Mukwazhi, File)
PHOTO: Tsvangirayi Mukwazhi/AP
FILE - In this April 7, 2016 file photo Zimbabwean President Robert Mugabe attends a meeting with the country's war veterans in Harare. Mugabe seemed almost untouchable for much of his nearly four-decade rule. Shrewd and ruthless, he managed to stay in power despite advancing age, growing opposition, international sanctions and the dissolving economy of a once-prosperous African nation. Now, the apparent abrupt end of the Mugabe era is launching Zimbabwe into the unknown. It's a humbling close to the career of a man who crushed dissent or sidelined opponents after leading Zimbabwe since 1980. (AP Photo/Tsvangirayi Mukwazhi, File)
Now playing
01:11
Zimbabwe's ruling party fires Mugabe
(CNN) —  

Zimbabwe’s pursuit of stability appeared uncertain Friday after the country’s main opposition leader said his party would challenge the results of the presidential election, labeling them “fraudulent and illegal.”

A day after President Emmerson Mnangagwa was declared the winner of the vote, Nelson Chamisa, leader of the Movement for Democratic Change, told a news conference the vote was “anything but a free and fair.”

The landmark vote – Zimbabwe’s first since the toppling of strongman Robert Mugabe – was being closely watched, with election observers and foreign investors looking on to see if the country had shed its previous reputation.

Opposition leader Nelson Chamisa says his party will challenge the election results.
PHOTO: JEKESAI NJIKIZANA/AFP/Getty Images
Opposition leader Nelson Chamisa says his party will challenge the election results.

Chamisa, who at 40 is the country’s youngest presidential candidate, said his party was working “around the clock with a legal team” to put together a plan of action following the results, but he did not give any details.

“As far as we are concerned this presidential result is fraudulent, illegal, illegitimate, and characterized by serious credibility gaps and some serious legitimacy issues that we feel must be raised,” Chamisa said at the news briefing.

The opposition leader’s first attempt to hold a press conference Friday was thwarted after police stormed the Harare hotel where he was scheduled to speak.

Zimbabwe anti-riot police personnel deploy Friday at the Bronte Hotel in Harare.
PHOTO: ZINYANGE AUNTONY/AFP/Getty Images
Zimbabwe anti-riot police personnel deploy Friday at the Bronte Hotel in Harare.

For reasons that were unclear, police escorted journalists away from the area.

A Movement for Democratic Change representative told CNN the police had broken it up because they thought it was an “illegal political gathering.”

After a brief standoff, police allowed accredited journalists back into the hotel.

President Emmerson Mnangagwa has defended the vote as "a free, fair and credible election."
PHOTO: Tsvangirayi Mukwazhi/AP
President Emmerson Mnangagwa has defended the vote as "a free, fair and credible election."

Mnangagwa condemned the police action, tweeting: “The scenes today at the Bronte Hotel have no place in our society and we are urgently investigating the matter to understand exactly what happened. Over the past nine months we have protected freedom of speech, of assembly and the right to (criticize) the government.”

Following Chamisa’s news conference, Mnangagwa called for peace and unity.

Speaking at the State House in Harare, he said, “We cannot allow violent actions of few to detract from democratic expression of the many.”

Mnangagwa sought an independent commission to investigate violent clashes this week and defended the vote as “a free, fair and credible election.”

“Whoever you voted for, now begins the time to join hands for us to forge for a better future,” he said.

“I pray to be a listening president, a fair president, a responsible and inclusive president.”

On Wednesday, six people died following clashes between security forces and protesters in the capital as opposition supporters alleged vote rigging following the release of partial parliamentary election results.

Supporters celebrate after Mnangagwa is declared the winner in Zimbabwe's landmark election.
PHOTO: LUIS TATO/AFP/Getty Images
Supporters celebrate after Mnangagwa is declared the winner in Zimbabwe's landmark election.

The country is anxious to ensure the elections are considered free and fair to lure back foreign investment and resuscitate its ailing economy.

Zimbabwe, which suffered crippling hyperinflation under Mugabe, needs the International Monetary Fund to start giving it loans again. It also needs the United States, European Union and others to lift sanctions.

On Friday, US State Department spokeswoman Heather Nauert said that “Zimbabwe’s success in delivering an election day that was peaceful, and open to international observers, was subsequently marred by violence and a disproportionate use of deadly force against protestors by the security forces.”

Nauert’s statement said the US will review voting data collected by international and local observation teams to make a complete assessment of the election.

Mnangagwa – who according to the election commission late Thursday won 50.8% of the vote – took power in November after helping orchestrate a de facto coup against Mugabe who had served with for decades.

Known as “the crocodile” for his political cunning and longevity, the 75-year-old has tried to rebrand the ruling Zanu-PF party, pledging to heal divisions and rebuild the country.

But Mnangagwa is widely considered to represent a continuation of Mugabe’s rule because he worked closely with the former leader for more than 40 years, first as his special assistant during the 1977 liberation war, and later as security minister and justice minister.

’Biggest challenges’

On Friday, South African President Cyril Ramaphosa called on all parties to accept the election results and “follow legal remedies provided for in the constitution and electoral law.”

In a statement, Ramaphosa said he had called and congratulated Mnangagwa and expressed a commitment to “enhance the historical, political and fraternal relations which exist between South Africa and Zimbabwe.”

The statement is likely to be interpreted as an important endorsement for Mnangagwa as he looks to defuse tensions and consolidate his victory.

European Union election observers on Friday also urged that the results be fully explained to the public.

Elections observers from the European Union and the African Union have been monitoring proceedings.
PHOTO: Jerome Delay/AP
Elections observers from the European Union and the African Union have been monitoring proceedings.

“One of the biggest challenges this election faces is a lack of trust in all aspects,” Mark Stevens, deputy chief observer of the EU Election Observation Mission to Zimbabwe, told CNN.

“We think now that the result has been given, we stress very strongly it needs to be fully explained how this result was ascertained, broken down by constituency, by polling station, so everyone can see how the result was ascertained and be confident about it, particularly as the gap was quite narrow.”

Police block a road leading to the opposition offices Thursday in Harare.
PHOTO: Tsvangirayi Mukwazhi/AP
Police block a road leading to the opposition offices Thursday in Harare.

Stevens also said his group had noted voter intimidation, media bias, misuse of resources and an imbalance in funding as some of the problems ahead of and during the vote.

CNN’s David McKenzie and Brent Swails reported from Harare, and James Masters wrote from London. Bard Wilkinson and Columbus Mavhunga contributed to this report.