Tehran, Iran (CNN) A suicide bombing hit a bus carrying members of the Iranian military's elite Revolutionary Guard in the southeastern province of Sistan-Baluchestan, killing at least 23 and wounding 17, according to the semiofficial Fars News Agency.

Iranian state media has offered differing death tolls for the attack, ranging from 27 to 41.

A separatist group called Jaish al-Adl, or Army of Justice, has claimed responsibility, according to state-run news agency IRNA.

The incident took place on a desert road near Iran's volatile border with Pakistan and Afghanistan, where the group is known to operate. It comes two days after Iran marked the 40th anniversary of the Islamic Revolution.

The truck was loaded with explosives when it detonated and struck the bus carrying members of the guard who were coming back from "a border guarding mission," Fars reported.

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