Yemen’s President Abed Rabbo Mansour Hadi was forced to flee his residence in the city of Aden on Wednesday as Houthi militants advanced on the president's latest stronghold, anonymous officials told the Associated Press. In the attack, the rebels reportedly captured Yemen’s defense minister.

Hadi fled the port city where he established his temporary capital for an undisclosed location just hours after a Houthi-held TV station announced that the rebels had seized an air base that was used by U.S. forces in the fight against al Qaeda.

The anonymous officials said they saw Hadi’s presidential convoy leaving the palace. Hadi's forces reportedly did not offer any official comment.

This is the second time Hadi has had to flee before the militants’ advances. He had considered Aden the legitimate capital of Yemen after fleeing there in February from the constitutional capital of Sanaa, which was captured by Shia Houthi rebels in September. Since then, he has withdrawn his resignation as president and attempted to garner support from local military groups and governors, as well as international Gulf allies.

The area around Aden has seen heavy fighting between forces loyal to Hadi, and Houthi militants and allied armed groups who fight for former President Ali Abdullah Saleh. Earlier on Tuesday, Hadi’s forces lost the vital port of al-Mukha and parts of the city of Taiz in a standoff with the Houthi rebels.

Houthi officials said their hostilities were reserved for Hadi and his forces alone. "We are not targeting Aden, the South or any other region, just takfiri [Sunni fundamentalist] groups that are in some areas allied with various political forces," Houthi official Mohammed al-Bukhaiti told Reuters.

Hadi had urgently requested on Sunday that the U.N. authorize the use of force against the Houthis, after a Thursday attack on Aden’s airport left 13 dead and dozens wounded, in what he called “a pure act of aggression on the Yemeni people and the constitutional legitimacy, as well as an assault on Yemen's sovereignty and security."

The next day, suicide bombings in Sanaa against Shiite mosques, which follow the Houthis’ Zaidi sect of Islam, killed at least 130 people and wounded over 300, including the death of at least one prominent Houthi leader.

The U.N. Security Council had unanimously demanded that the Houthis withdraw from Yemen and cede power to Hadi, but the resolution does not authorize the use of force. Jamal Benomar, U.N. special adviser on Yemen, warned on Sunday that the country is heading “to the edge of civil war,” and urged all parties to seek diplomatic solutions.

Diplomatic missions from Gulf countries including Saudi Arabia, the United Arab Emirates and Kuwait relocated to Aden after withdrawing from Houthi-held Sanaa, but they have reportedly evacuated their missions again as the fighting intensified.