US raid on al-Qaeda Yemen cell kills 57 people
Eight women and eight children were among those killed in the dawn raid in Yakla district, in the central province of Baida, said the provincial official, who did not want to be named, and tribal sources.
Sources in the region said the raid targeted the houses of three tribal chiefs linked to al-Qaeda.
The provincial official said Apache helicopters also struck a school, a mosque and a medical facility which were all used by jihadi militants.
Other sources spoke of US commandos taking part in the operation, but it was not possible to verify the information.
The three prominent tribal figures killed in the attack were identified as brothers Abdulraouf and Sultan al-Zahab and Saif Alawai al-Jawfi, the official and other sources said.
They were known for their strong links to al-Qaeda, the sources said.
The Zahab brothers have two other al-Qaeda brothers who were also killed in the past by drone strikes.
An al-Qaeda chief in the region, who was identified as foreigner Abu Barazan, was also killed in the attack, the official said.
The military operation is the first to be attributed to the United States against militants in Yemen since Trump took office on 20 January.
Under Trump's predecessor Barack Obama, the United States stepped up its use of drone strikes against suspected militants in Yemen, as well as other countries including Afghanistan.
The US considers the extremist group's Yemen-based franchise, al-Qaeda in the Arabian Peninsula, to be its most dangerous.
Although it only sporadically reports on a long-running bombing campaign against al-Qaeda in the Arabian Penunsula, it is the only force known to be operating drones over Yemen.
On 14 January, the Pentagon announced the killing of a senior al-Qaeda operative in Baida the week before in an air strike.
Al-Qaeda and the Islamic State group have exploited a power vacuum created by the two-year-old conflict in Yemen between the government and Houthi rebels, especially in the country's south and southeast.
Baida province is mostly controlled by the Houthis, but Yakla is ruled by the tribes, and has at least two training bases for al-Qaeda, local sources said.
Forces loyal to President Abd Rabbo Mansour Hadi have mounted offensives against jihadists in the south, but the militants remain active in several areas.
The conflict in Yemen has killed more than 7,400 people since a Saudi-led Arab coalition intervened to support Hadi in March 2015, according to the World Health Organization.
But UN humanitarian coordinator Jamie McGoldrick said last week that as many as 10,000 civilians may have died.