Donald Trump left the White House on Marine One in an unannounced trip to pay respect to a US Navy Seal killed in Yemen.

Speculation surrounded the US president's unexpected departure as the White House had not disclosed the destination of his flight.

Mr Trump travelled to Dover Air Force Base in Delaware in an unexpected visit to meet the family of William "Ryan" Owens, a US commando who died in a raid on al-Qaeda in Yemen that went wrong.

The military operation was the first to be authorised by the former reality TV star.

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The US military said 14 militants were killed in the raid on al-Qaeda. Three other commandos were injured.

The Pentagon did not confirm or deny reports from medics on the ground and in Yemeni media that up to 30 people, including 10 women and children, were killed.

US military officials told Reuters Mr Trump approved his first covert counter-terrorism operation without sufficient intelligence, ground support, or adequate backup preparations.

As a result, three officials said, the attacking Seal team found itself dropping onto a reinforced al-Qaeda base defended by landmines, snipers, and a larger than expected contingent of heavily armed Islamist extremists.

They said the extremists' base had been identified as a target before the Obama administration left office on 20 January, but then-President Barack Obama held off on approving a raid, in part because officials said they were not certain the available intelligence was sufficiently reliable.

Also, on-the-ground surveillance of the compound was "minimal, at best," one of the officials said.

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White House officials were not immediately available to comment about the officials' characterization of the raid.

All three officials said "a brutal firefight" took the lives of Mr Owens and at least 15 Yemeni women and children. One of the dead was the eight-year-old daughter of the late militant Anwar al-Awlaki, who was killed by a 2011 US drone strike.

Some of the women were firing at the US force, Pentagon spokesman Captain Jeff Davis told reporters.

The American elite forces did not seize any militants or take any prisoners offsite but White House spokesman Sean Spicer said the raid yielded benefits.

"Knowing that we killed an estimated 14 [al-Qaida] members and that we gathered an unbelievable amount of intelligence that will prevent the potential deaths or attacks on American soil - is something that I think most service members understand, that that's why they joined the service," Mr Spicer said.