Phnom Penh, Cambodia (CNN) -- The opposition party in Cambodia has rejected the results of the country's national election, which handed another win to long-serving Prime Minister Hun Sen.
The Cambodia National Rescue Party (CNRP) said Monday the weekend balloting was marred by irregularities, and demanded an investigation.
Cambodians went to the polls Sunday.
According to preliminary results released by the national election commission, the opposition won 55 seats. But the number wasn't large enough to unseat the ruling Cambodian People's Party, which won 68 seats.
In a statement, opposition leader Sam Rainsy said a committee -- made up of representatives of the main political parties, the election commission and foreign election monitors -- should look into "all serious election irregularities."
Once the committee issues its findings, political leaders from both sides will find ways to "redress the injustice done to the Cambodian people whose will has been distorted for too long," he said.
Hun Sen has been in office for 28 years.
Still, opposition groups were energized.
The two main parties teamed up to form the CNRP, and hoped for strength in numbers: Enough votes to take over control from the ruling party.
More than 9 million people were eligible to vote.
The excitement bubbled over Friday when Rainsy returned home from exile in France.
He left in 2009 to avoid prison on charges of spreading disinformation -- charges many considered politically motivated. International pressure led to him receiving a royal pardon last week. But he arrived too late to run for office.
The national election committee said it worked hard to ensure the election was far.
"In preparing for the election this year, we started in the middle of 2012," said Tep Nytha, the secretary general of the committee, ahead of the balloting.