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American photojournalist Luke Somers, held hostage in Yemen, was killed by al Qaeda during a "dangerous" rescue bid, his family and the White House said Saturday.

U.S. Special Operations Forces conducted a mission on White House orders amid "compelling reasons" to believe Somers' life was in imminent danger, Defense Secretary Chuck Hagel said in a statement. Another hostage, South African Pierre Korkie, was also killed in the operation.

President Barack Obama condemned the killing of British-born U.S. citizen Somers as "barbaric."

Somers' sister, Lucy, told NBC News' U.K. partner ITV News that the FBI had informed the family of the 33-year-old's death. They declined to be interviewed.

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Somers, a teacher and photographer, was abducted a year ago in Sanaa where he had been working as a freelance photographer for the Yemen Times.

Friday's operation took place in Shabwa province, a Yemen interior ministry official told NBC News, adding that several militants were also killed.

It came two days after the Pentagon acknowledged an earlier U.S. commando mission to rescue Somers had also failed. Al Qaeda posted a video Thursday that showed Somers and a local militant commander threatening that the hostage would meet his fate in three days if the U.S. didn't meet the group's demands.

Because Somers’ life was in “imminent danger,” 40 special U.S. forces executed the “high-risk” mission to rescue him, but found him and Korkie gravely wounded when they arrived, a senior U.S. military official told NBC News. The two had apparently been shot by their captors. The men were loaded onto a U.S. medevac helicopter, but both succumbed to their wounds.

"The United States strongly condemns the barbaric murder of Luke Somers at the hands of al Qaeda terrorists during a rescue operation conducted by U.S. forces in Yemen in partnership with the Yemeni government," Obama said in his statement. "On behalf of the American people, I offer my deepest condolences to Luke's family and to his loved ones."

#AQAP source says 2 hostages were killed by the group "before leaving location" during a US rescue mission in #Yemen. Rescue took 3 hours. - Zaid Benjamin (@zaidbenjamin) December 6, 2014

Obama added: "I also offer my thoughts and prayers to the family of a non-U.S. citizen hostage who was also murdered by these terrorists during the rescue operation. Their despair and sorrow at this time are beyond words. It is my highest responsibility to do everything possible to protect American citizens."

Hagel's statement said: "Yesterday's mission is a reminder of America's unrelenting commitment to the safety of our fellow citizens - wherever they might be around the world. I commend the troops who undertook this dangerous mission. Their service and valor are an inspiration to all of us."

At least half a dozen al Qaeda captors were killed during a brief exchange of gunfire during the raid, a senior U.S. official said. None of the U.S. commandos involved in the mission were wounded, the official said.

We received news that Pierre was killed in an attempt by American Special Forces, early hours this morning, 2free hostages in Yemen. - Gift of the Givers (@GiftoftheGivers) December 6, 2014

Disaster relief group Gift of the Givers said it had "received with sadness the news that Pierre [Korkie] was killed in an attempt by American Special Forces, in the early hours of this morning, to free hostages in Yemen."