Hadi had been under house arrest for a month after he resigned under pressure from Houthi rebels. But he escaped and released a statement saying he is still president, calling all political decisions made since September illegal and invalid.
A nephew of the president was kidnapped Sunday by Houthi rebels, two security officials in Ibb province told CNN. The nephew, Nasser Ahmed Mansour Hadi, was heading to the seaport province of Aden, where the President fled after escaping from house arrest in the capital, Sanaa.
Protesters called for Hadi to stand against the Houthi coup. Sanaa saw the largest demonstrations urging Hadi to end militant occupation of Sanaa.
"The Houthis thought they could not be stopped, and it only took hours for them to fall in the eyes of the people. Yemen has a president and the people will stand with him to uproot the Houthi militants from Sanaa," Ali Al-Saedi, a protest organizer in Sanaa, told CNN.
In Taiz, tens of thousands took to the streets to show support for the legitimacy of the president and condemn the continued Houthi takeover of the capital.
They carried placards reading "Out to militant rule, return of government institutions."
Last month, Houthis attacked the presidential palace and ministerial Cabinet, forcing both the president and prime minister to resign. Houthi militants then put Hadi under house arrest.
Since then, Houthis have failed to form a government or reach a deal with other political factions for the formation of a presidential council.
Resignation was never accepted by parliament
The militants tightened their grip on power over the last month, but the House of Representatives has not met to accept Hadi's resignation.
Hours after Hadi fled Sanaa on Saturday, Houthi officials tried to force parliamentarians to meet immediately to accept his resignation, but their efforts failed.
The ruling General People's Congress party, headed by Yemen's former President Ali Abdullah Saleh, which holds a majority of seats in parliament, said it will not push for a parliament vote to accept the resignation of Hadi.
"Hadi is the President of Yemen, since his resignation has yet to officially reach parliament. Yemen is still led by a constitutional elected president," said Abdul Aziz Jubari, the secretary general of the independent Justice and Building Party.
Houthis are Shiite Muslims who have long felt marginalized in the majority Sunni Muslim country. They had been at war with the central government for more than a decade, but their entry into Sanaa in September brought things to a head, sparking battles that left than 300 people dead before a ceasefire was agreed to that month. Houthis then pressured Hadi to step down last month after he refused to agree to certain political demands.
The Houthis' takeover of Sanaa stunned governments of Western nations, which pulled out diplomatic staff this month.
Houthis arrest own security personnel after escape
As part of an investigation into Hadi's escape, Houthis on Saturday arrested dozens of their own security personnel who were responsible for watching him, a senior Houthi official said.
Houthis arrested two people connected to Hadi -- his media secretary Yahya Al Arassi and his private physician -- after his escape, one of Hadi's advisers said.
A senior official with a Sunni political party opposed to the Houthi takeover said that he backs Hadi's claim to the presidency.
"Hadi's withdrawal (of his resignation) would save the country and end the Houthi oppression of the Yemeni people," said Mohammed Al-Sabri, senior official of the Nasserite party.
There already had been resistance to the Houthis' attempted takeover of national government institutions from different groups in Yemen, particularly in the South, where there's a long-running secessionist movement.
Also opposed to the Houthis is the Sunni terror group al Qaeda in the Arabian Peninsula, which exerts influence over many rural areas across the country. AQAP vowed to attack Houthi loyalists nationwide last year.
Yemen's political turmoil could have an impact on the United States' fight against AQAP. The United States has long had a relationship with Yemen's leaders, working with them to target AQAP militants.
It's not clear what the Houthis' takeover of Sanaa means for U.S. anti-terrorism efforts, but the drone program there still appears to be active. A U.S. drone strike killed senior AQAP cleric Harith bin Ghazi al-Nadhari and three other people in Shabwa province on January 31.