The exact cause of the blast is still unknown. Governor Mehmet Kiliclar said the attack was caused by a car bomb. A statement released by Turkey’s military said that army vehicles were targeted when they were stopped at a traffic light, according to the AP. The attack reportedly occurred near the Turkish parliament building.

No person or group has claimed responsibility for the attack at the time of publication. Some have speculated that the attack resembles the similar attacks on buses by the Kurdistan Workers’ Party (PKK), an armed rebel group that has challenged the Turkish government since the 1980s.

The Turkish government reportedly blocked the use of Facebook and Twitter after the attack.