American photojournalist Luke Somers was killed during a failed rescue attempt

American photojournalist Luke Somers was killed during a failed rescue attempt in Yemen, Defense Secretary Chuck Hagel said Saturday.

Somers had been held by al-Qaeda militants following his abduction in Yemen's capital of Sanaa in September 2013.

Hagel, speaking from Kabul where he made a surprise visit Saturday, confirmed the British-born hostage's death following an unsuccessful raid to free him by U.S. and Yemeni special forces.

"There were compelling reasons to believe Mr. Somers' life was in imminent danger," Hagel said in a statement, describing Somers' death as murder at the hands of terrorists.

Lucy Somers said she learned of her brother's death from the FBI.

"We ask that all of Luke's family members be allowed to mourn in peace," she told the Associated Press.

A second hostage, South African Pierre Korkie, a teacher abducted in Yemen in May 2013 with his wife, was also killed in the failed raid. Yolande Korkie had previously been released by Al-Qaeda in the Arabian Peninsula militants.

During the rescue operation, helicopters swept in and dropped U.S. commandos about a mile from the village where Somers was being held hostage, according to a senior Defense Department official who spoke on condition of anonymity because he was not authorized to speak publicly.

U.S. warplanes flew overhead for protection but did not fire weapons. The commandos, from teams based in the Middle East, killed all of the al-Qaeda-linked terrorists. No U.S. forces were wounded, the official said.

President Obama said he authorized the rescue attempt because of information the U.S. had that Somers' life was in immediate danger, including a video released by his terrorist captors earlier this week that announced the journalist would be killed within 72 hours.