Missiles fired by a U.S. drone slammed into a convoy of vehicles traveling to a wedding party in central Yemen on Thursday, killing at least 13 people, Yemeni security officials said.

The officials said the attack took place in the city of Radda, the capital of Bayda province, and left charred bodies and burnt out cars on the road. The city, a stronghold of al-Qaida militants, witnessed deadly clashes early last year between armed tribesmen backed by the military and al-Qaida gunmen in an attempt to drive them out of the city.

There were no immediate details on who was killed in the strike, and there were conflicting reports about whether militants were traveling with the wedding convoy.

A military official said initial information indicated the drone mistook the wedding party for an al-Qaida convoy. He said tribesmen known to the villagers were among the dead.

One of the three security officials, however, said al-Qaida militants were suspected to have been traveling with the wedding convoy.

The CIA declined to comment on the reported drone strike. Although 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.