The CIA declined to comment on the reported drone strike. While the U.S. acknowledges its drone program in Yemen, it does not usually talk about individual strikes.
If further investigations determine that the victims were all civilians, the attack could fuel an outburst of anger against the United States and the government in Sanaa among a Yemeni public already opposed to the U.S. drone strikes.
Civilian deaths have bred resentments on a local level, sometimes undermining U.S. efforts to turn the public against the militants. The backlash in Yemen is still not as large as in Pakistan, where there is heavy pressure on the government to force limits on strikes but public calls for a halt to strikes are starting to emerge.
In October, two U.N. human rights investigators called for more transparency from the United States and other countries about their drone programs, saying their secrecy is the biggest obstacle to determining the civilian toll of such strikes.
The missile attacks in Yemen are part of a joint U.S.-Yemeni campaign against al-Qaida in the Arabian Peninsula, which Washington has called the most dangerous branch of the global terrorist network.
Thursday's drone strike is the second since a massive car bombing and coordinated assault on Yemen's military headquarters killed 56 people, including foreigners. Al-Qaida claimed responsibility for the attack, saying it was retaliation for U.S. drone strikes that have killed dozens of the group's leaders.
Security forces in the Yemeni capital boosted their presence Thursday, setting up checkpoints across the city and sealing off the road to the president's residence, in response to what the Interior Ministry called threats of "terrorist plots" targeting vital institutions and government buildings.
Meanwhile, in the Yemen's restive northern, ultraconservative Sunni Muslim militants and rebels belonging to a branch of Shiite Islam battled each other with artillery and machine guns in clashes that killed more than 40 people, security officials said.
The violence between Islamic Salafi fighters and Hawthi rebels has raged for weeks in Yemen's northern province of Saada, but the latest sectarian clashes marked an expansion of the fighting to the neighboring province of Hagga. The government brokered a cease-fire last month to try to end the violence, but both sides have repeatedly broken the truce.
Officials said clashes began when ultraconservative Salafis took over a Hawthi stronghold in a mountainous area near the border with Saudi Arabia. The officials say that most of the casualties were on the Hawthi side.
The officials said that Salafis, however, accused Hawthis of trying to infiltrate their strongholds in the town of Fagga.
The officials spoke on condition of anonymity because they weren't authorized to discuss the fighting publicly.
Hawthi launched in insurgency in 2004 against autocratic President Ali Abdullah Saleh, who stepped down in 2012 after a popular uprising against his rule. Over the course of the Hawthi rebellion, hundreds of people were killed and an estimated 125,000 people uprooted until the rebels and the government struck a fragile cease-fire in 2010.
But the north remained restive despite the truce, and fighting flared along another fault line in November after Hawthis accused the Salafis of trying to gain a foothold in their territory by spreading their brand of Islam.
The rebels say their community of Shiite Muslims suffers discrimination and neglect and that the government has allowed ultraconservative Sunni extremists too strong a voice in the country. Hard-line Sunnis consider Shiites heretics.
