Amnesty International has warned that Iranian authorities are about to execute a man convicted of killing three police officers during clashes involving members of a Sufi order.

The British-based rights group said in a statement on June 17 that relatives of Mohammad Reza Salas had been summoned to the prison where he is being held for a final visit.

Amnesty said this suggests he could be executed within hours.

During clashes in Tehran in February, Salas rammed a bus into a group of police officers during battles between security forces and followers of the Sufi Gonabadi order, known as dervishes.

The dervishes were protesting the arrest of members of the sect, as well as rumors that their 90-year-old leader would soon be detained by police, despite assurances by the authorities that they had no such intention.

During court hearings in March, Salas said repeatedly that he did not kill the police officers intentionally, according to local media.

Two members of the paramilitary Basij force were also killed in the skirmishes, authorities said. Some 300 dervishes were reportedly arrested following the violence.

Sufism, a mystical branch of Islam, is not illegal in Iran, but rights groups accuse the Iranian government of harassment and discrimination against their followers, including the Gonabadis, one of the largest Sufi sects.