Aden: Elite US forces launched a dawn raid against Al-Qaeda in Yemen on Sunday, killing at least 14 suspected jihadists in an operation in which an American soldier also died.
US President Donald Trump said Americans were saddened at the news of the death of a "heroic service member".
The assault marked Washington's first major military action in Yemen under Trump, who has vowed to step up the US fight against Islamic extremism.
The US military said the raid in the Yakla region of Baida province killed 14 members of Al-Qaeda in the Arabian Peninsula (AQAP), which Washington views as the global network's most dangerous branch.
A Yemeni provincial official gave a higher toll of 41 presumed terrorists and 16 civilians killed in the raid, including eight women and eight children.
Washington did not specify how the US soldier died. It said three more American servicemen were injured in the raid along with a fourth who was hurt in a "hard landing".
"Americans are saddened this morning with news that a life of a heroic service member has been taken in our fight against the evil of radical Islamic terrorism," Trump said.
He said in a statement that sacrifices by the armed forces "are the backbone of the liberty we hold so dear as Americans, united in our pursuit of a safer nation and a freer world."
A statement from US Central Command said that an aircraft used in the raid had to be "intentionally destroyed".
A US defence official told AFP that "no prisoners had been taken" during the operation.
- Tribal chiefs -
A civil war in Yemen between Iran-backed rebels and pro-government forces has killed more than 7,000 people since March 2015 and allowed extremists including AQAP and the ISIS group to gain ground in the impoverished nation.
Fierce clashes between Yemeni loyalists and the Shiite rebels have killed more than 100 fighters in the past 24 hours on Yemen's west coast, officials said on Sunday.
Sunday's US raid was said to have targeted the houses of three tribal chiefs linked to Al-Qaeda.
The provincial official said Apache helicopters also hit a school, a mosque and a medical facility which were all used by Al-Qaeda militants.
The three prominent tribal figures with known Al-Qaeda links killed in the attack were identified as brothers Abdulraouf and Sultan al-Zahab and Saif Alawai al-Jawfi, the official and other sources said.
Among the children killed in the raid was the daughter of slain US-born preacher Anwar al-Awlaqi, Nura, who lived with the family of her maternal uncle, a relative said.
Awlaqi himself was killed in September 2011 in a drone strike and his son Abulrahman was killed two weeks later in a similar attack.
Local officials said an Al-Qaeda chief in the region was also killed in Sunday's raid.
The operation, which Trump said "will assist the US in preventing terrorism against its citizens and people around the world", was the first major US military action in Yemen since he took office on January 20.
- 'Heinous crime' -
A statement from AQAP said that 30 people died in the raid -- "only women and children... with some tribal leaders who have no connections" to the group, according to a translation provided by the SITE Intelligence Group.
AQAP claimed an Apache helicopter fired more than a dozen rockets at three houses in the area, condemning what it called a "heinous crime".
Under Trump's predecessor Barack Obama, the US dramatically increased its use of drone strikes against suspected jihadists in Yemen, as well as other countries including Afghanistan.
Although the US only sporadically reports on its long-running bombing campaign against AQAP, it is the only force known to operate armed drones over Yemen.
On January 14, the Pentagon announced the killing of a senior Al-Qaeda operative in Baida the week before in an air strike.
Yemen's long-running conflict escalated in March 2015 when a Saudi-led coalition began bombing raids against Huthi rebels who had stormed the capital and taken swathes of central and northern territory.
Around 7,400 people have died in air strikes and clashes since then, the UN says, and aid agencies have warned of an impending humanitarian crisis in the Arab world's poorest nation.
Baida province is mostly controlled by the Huthis, but Yakla is ruled by tribes, and has at least two training bases for Al-Qaeda, local sources said.
Forces loyal to President Abedrabbo Mansour Hadi have mounted offensives against jihadists in the south, but the militants remain active in several areas.