A U.S. drone strike in Yemen, the first so far this year, killed three Al Qaeda fighters on Monday, signaling Washington's determination to keep targeting the global terror network's most lethal branch despite the resignation of the Yemeni president, a top U.S. ally, in the face of a Shiite rebel power grab.

Hours later, the State Department announced the U.S. Embassy in Yemen was closing to the public "until further notice" over security concerns as street gunbattles and political turmoil continue to roil this impoverished Arab country.

The drone strike was also the first such U.S. action since Shiite rebels known as Houthis placed embattled President Abed Rabbo Mansour Hadi and his Cabinet under house arrest last week in an attempt to force them to make political concessions. After reaching a tentative deal with the Houthis, the president and his government resigned in an effort to thwart rebel attempts to force more compromises.

Yemeni tribal and security officials in the central province of Marib said a missile hit a vehicle carrying three men near the boundary with neighboring Shabwa province, an Al Qaeda stronghold.

An Al Qaeda member told The Associated Press that one of the three slain fighters was Saudi while the other two were Yemenis. He identified the Saudi man as Awaid al-Rashidi, who he said was in his 30s and had been imprisoned in Saudi Arabia for seven years, apparently over terrorism charges. The two Yemeni Al Qaeda members killed in the strike were Abdel-Aziz al-Sanaani and Mohammed al-Jahmi from Marib's tribe of Jahmi, the member said.

Both Yemeni officials and the Al Qaeda member spoke on condition of anonymity because they were not authorized to speak to media.

The Houthis, who claim to only want an equal share of power, had seized the capital of Sanaa and its central province in September and at least eight other provinces, after descending from their northern stronghold.

The prospect of a leaderless Yemen has raised concerns about Washington's ability to continue targeting Al Qaeda in the Arabian Peninsula, as the Yemeni branch is known. The group claimed the recent attack on a French satirical weekly and has mounted several failed attacks on the U.S. homeland.

The Houthis are staunch opponents of Al Qaeda but as the Shiite rebels push into Sunni-dominated areas they risk driving locals into the arms of the insurgents.

The strike came one day after U.S. President Barack Obama defended his counterterrorism strategy in Yemen, saying his approach "is not neat and it is not simple, but it is the best option we have." He ruled out deploying U.S. forces there.

Last year at least 23 drone strikes killed 138 Al Qaeda militants as well as some civilians, according to the Long War Journal, which tracks militant groups. U.S. officials rarely comment on the covert drone program.

The Houthis insist they merely want a new power-sharing arrangement with rival political factions. Critics say they want to retain Hadi as president in name only, while keeping an iron grip on power. They also accuse the Houthis of being a proxy of Iran, an allegation the rebels deny.