US officials have said they had no choice but to launch a special forces rescue operation in Yemen that ended with Al-Qaeda killing an American photojournalist and a South African teacher.
The hostages -- 33-year-old American Luke Somers and 57-year-old South African Pierre Korkie -- were killed by their captors when US commandos stormed an Al-Qaeda hideout early on Saturday.
The failed raid came after the kidnappers had threatened to kill Somers within 72 hours, and just a day before Korkie was due to be released under a negotiated deal.
Calling the murders "barbaric," President Barack Obama said he had authorised the rescue attempt because the video and other information "indicated that Luke's life was in imminent danger".
"The United States will spare no effort to use all of its military, intelligence, and diplomatic capabilities to bring Americans home safely, wherever they are located," he said.
A senior US defence official said there were "good indications" that Al-Qaeda in the Arabian Peninsula, the group's powerful Yemeni branch, "were preparing to kill" Somers.
"It was either act now and take the risk, or let that deadline pass. And no one was willing to do that," said the official, who was with US Defence Secretary Chuck Hagel in the Afghan capital Kabul.
British-born Somers, 33, had worked as a freelance photographer for the BBC and spent time at local newspapers, including the Yemen Times, before being abducted in Sanaa in September 2013.
- 'Lost element of surprise' -
Korkie and his wife Yolande, who had worked as teachers in Yemen for four years, were kidnapped by Al-Qaeda in May 2013.
She was released in January and the Gift of Givers charity said logistical arrangements had already been put in place to fly Korkie out of Yemen on Sunday.
Saturday's operation saw 40 US commandos dropped by helicopter in the dead of night 10 kilometres (six miles) from where Somers and Korkie were being held in the southeastern province of Shabwa, officials said.
They made their way to the Al-Qaeda hideout by foot, but were discovered about 100 metres (yards) away.
A short but intense firefight -- lasting five to 10 minutes -- erupted, the US defence official said.
At least five militants were believed killed, and there were no casualties among US personnel.
"When the element of surprise was lost, and a firefight ensued, we believe that is when (the hostages) were shot," the official said.
The US has said Navy SEALs and Yemeni commandos had already tried unsuccessfully to rescue Somers last month, but the Pentagon would not confirm which branch of the special forces took part this time.
It said national forces did not join the latest raid but that Yemen was consulted and supported the operation.
One hostage -- it was not clear who -- died en route to the USS Makin Island off Yemen, and the other died on the operating table, officials said.
Friends and family described Somers as a committed journalist who sought to document the lives of ordinary people amid turmoil.
- 'Home for Christmas' -
Yemen has been wracked by unrest since a 2011 uprising forced president Ali Abdullah Saleh to step down, with rival militias battling for control of parts of the impoverished country.
"Luke was a photojournalist who sought through his images to convey the lives of Yemenis to the outside world," Obama said.
Korkie's family had been expecting him home soon, said the Gift of Givers charity, which had been negotiating his release.
"The psychological and emotional devastation to Yolande and her family will be compounded by the knowledge that Pierre was to be released by Al-Qaeda tomorrow," it said on Saturday.
"Three days ago we told her 'Pierre will be home for Christmas'. We certainly did not mean it in the manner it has unfolded."
A US State Department official said Washington was aware two hostages were at the location but did not know the identity of the second.
The threat to kill Somers followed the murder since August of five Western hostages by the Islamic State jihadist group which controls parts of Syria and Iraq.
AQAP, considered one of the group's most dangerous affiliates, launches frequent attacks in Yemen and has also organised a series of attempted bomb attacks on Western targets.
Yemen is a key US ally in the fight against Al-Qaeda, allowing Washington to conduct a longstanding drone war against the group on its territory.