SANAA, Yemen — An American photojournalist and a South African teacher held by al-Qaida militants in Yemen were killed Saturday during a U.S.-led rescue operation that President Barack Obama said he ordered because of "imminent danger" to the U.S. hostage. U.S. officials believe the militants shot the two men during a firefight, and that both were alive when American forces pulled them from a building on the group's compound and put them on aircraft, where medical teams operated on them during a short flight to the USS Makin Island, a Navy ship in the region. South African Pierre Korkie is believed to have died during the flight, while American Luke Somers died on the ship, according to senior U.S. officials who spoke on condition of anonymity because the information had yet to be approved for release.