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While John Kerry sits face to face with the Iranians in Switzerland.

CAIRO — A Yemeni air base used by American forces for counterterrorism operations came under attack by army units and fighters allied with the Houthi movement on Wednesday as they clashed with forces loyal to President Abdu Rabbu Mansour Hadi near his current refuge in the southern city of Aden.

A satellite television network linked to the Houthi movement announced in the morning that its fighters had seized the base, Al Anad, north of Aden, and found it empty and looted. The Houthis said they had also captured two senior officials loyal to Mr. Hadi, including the defense minister. But those reports could not be confirmed.

Warplanes struck a location in Aden near Mr. Hadi’s compound around midday, and antiaircraft guns returned fire. Several news reports said that Mr. Hadi had left his home in Aden, possibly for fear of such an attack. There were conflicting reports early Wednesday about whether he had left the country as well, although few believe his departure would end the factional fighting.

The antiaircraft fire from the ground indicated that Mr. Hadi’s forces had not abandoned Aden. A television network controlled by the Houthis announced a $100,000 bounty for Mr. Hadi’s capture.

The United States evacuated its military personnel from Al Anad several days ago, with fighters from Al Qaeda’s Yemeni affiliate moving closer from one side and Houthi fighters pushing closer from the other.

Yemen is sliding toward a civil war with ominous elements of a sectarian feud, a regional proxy conflict, the attempted return of an ousted authoritarian, and the expansion of anti-Western extremist groups like Al Qaeda and the Islamic State eager to capitalize on the chaos.