Iran said Tuesday that at least three Pakistani citizens were among the assailants responsible for killing 27 members of the Islamic Revolutionary Guards Corps on a bus last week, including the driver of the explosives-laden car that rammed the vehicle.

The Feb. 13 bombing in a restive southeast region along the Pakistan border was one of the deadliest attacks in years to strike Iran. At least 13 people were wounded and the bus was destroyed, according to Iranian news websites.

Iran, which is predominantly Shiite Muslim, has often criticized Pakistan for harboring Sunni Muslim militants from the province, Sistan and Baluchistan, a haven for separatist groups and drug traffickers that have orchestrated attacks in recent years against Iranian security forces. But it is unusual for Iran to accuse Pakistani citizens.

The accusation, reported by Iran’s Tasnim news agency, was made by a commander of the Revolutionary Guards, Brig. Gen. Mohammad Pakpur, at a ceremony held Tuesday to honor victims of the attack.