A Syrian military bus exploded on Wednesday. There are conflicting reports on who was responsible for the incident.

A bus carrying Syrian military personnel exploded in the capital Damascus, killing the driver and injuring three others. The official SANA news outlet reported that the blast was the result of a short circuit that led to the bus’ gas tank blowing up.

The pro-opposition Syrian news outlet Enab Baladi reported that the Syrian al-Qaeda affiliate Hurras al-Din claimed responsibility for the bombing, citing a statement from the rebel group. Some Syrian observers on social media posted the same claim. The statement reads that Hurras al-Din had blown up the bus to kill Syrian military officers in the republican guard as revenge for recent fighting near the southern city of Daraa. Some other Arabic-language news outlets in Syria also published Hurras al-Din’s claim to the explosion.

The Syrian civil war began in 2011 following the government crackdown against the popular uprising against President Bashar al-Assad. The Assad government, backed by Iran and Russia, has retaken control of most of the country following earlier losses to rebel groups backed by Gulf states, Turkey and the United States. Rebel territory is now mostly confined to the northwest and small pockets of the south and east of the country.