A suicide bomber killed 41 members of Iran’s Armed Forces on a bus in southeast Iran on Wednesday, Iranian media reported. The attack, which targeted members of Iran’s Islamic Revolutionary Guards Corps, was among the deadliest attacks in Iran in years. The Guards quickly blamed the United States for the assault, which came during the 40th anniversary of the Islamic revolution that overthrew the American-backed shah in 1979. While the U.S. and Israel have accused Iran of instigating terrorism in the Middle East, Iran has also been the target of many terrorist attacks since the Islamic revolution.

Reports by the official Islamic Republic News Agency and the Fars News Agency said the victims had been traveling near the Pakistan border, a haven for militant separatist groups. A statement issued by the Revolutionary Guards said the bus had been “carrying the warriors of Islam soldiers who were returning from the region to their cities after completing their border mission.”