The 38 people, including 30 U.S. troops, killed in a helicopter crash in Afghanistan had been on a mission targeting a Taliban leader, sources told CNN. The deaths of the Americans, including 22 elite Navy SEALS, constituted the worst single-day toll on U.S. forces in the decade-long Afghan war. Their helicopter went down early Saturday in eastern Wardak province. The CNN report, quoting military officials, reported the Taliban commander they sought had been directly responsible for attacks on American forces. The SEALs were proceeding to help a Rangers unit under enemy fire in Wardak. Those killed in the crash also included a civilian and seven Afghan commandos. Combing operations continued at the wreckage site, said Lt. Col. Jimmie Cummings, spokesman for the International Security Assistance Force in Afghanistan. CNN quoted a military official as saying the majority of the SEALS who died in the crash were part of the unit that killed al-Qaida leader Osama bin Laden in the May 2 raid of his compound deep inside Pakistan. However, those dead did not include men involved in the bin Laden operation, the official said. The Taliban claimed it brought down the helicopter with a rocket-propelled grenade, but NATO declined comment on the details of the operation or the circumstances of the crash. Afghan President Hamid Karzai, who telephoned U.S. President Barack Obama to offer his condolences, called a security meeting of his top advisers to discuss the helicopter crash. Four other NATO soldiers died in separate incidents over the weekend in the east and the south, the report said. The incidents are occurring as NATO forces hand over security responsibilities to Afghan forces. The current timetable calls for the Afghan forces to take control of security for the entire country by 2014.