SANAA, Yemen — An American photojournalist and a South African teacher were killed Saturday during a high-risk, U.S.-led raid to free them from al-Qaida-affiliated militants in Yemen, a turbulent Arab country that is a centerpiece of U.S. counterterrorism efforts in the region.

The predawn raid was the second rescue attempt in as many weeks to free Luke Somers, a 33-year-old freelance photographer and editor kidnapped just over a year ago in Yemen’s capital.

South African Pierre Korkie, abducted 18 months ago with his wife in the city of Tazi, also was killed by militants as U.S. forces descended upon the militants’ compound in southern Yemen. A South African aid group trying to negotiate Korkie’s release said he was a day from freedom after a deal late last month that included a “facilitation fee” to the kidnappers. The relief organization had told Korkie’s wife that “the wait is almost over.”

President Barack Obama said he ordered the raid because Somers was believed to be in “imminent danger.” The president, in a statement, condemned Somers’ killing as a “barbaric murder,” but did not mention the 56-year-old Korkie by name, offering condolences to the family of “a non-U.S. citizen hostage.” The South African government said it was informed that Korkie died during the mission by American special forces.

“It is my highest responsibility to do everything possible to protect American citizens,” Obama said. “As this and previous hostage rescue operations demonstrate, 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.”

About 40 American special operations forces were involved in the rescue attempt, which followed U.S. drone strikes in the area, U.S. officials said. The rescuers, backed by Yemeni ground forces, advanced within 100 meters of the compound in Shabwa province when they were spotted by the militants. A firefight ensued.

Amid the fighting, U.S. forces saw a militant briefly enter a building on the compound. U.S. officials believe it was then that Somers and Korkie were shot. When Americans entered the building, they found both men alive, but gravely wounded.

Officials said that based on the location where Somers and Korkie were being held, there was no possibility that they were struck by American gunfire.

U.S. forces pulled Somers and Korkie onto V-22 Ospreys, and medical teams began performing surgery in midair. One hostage died during the short flight; the second died after the Ospreys landed on the USS Makin Island, a Navy ship in the region.