KABUL, Sept. 12 (Xinhua) -- Casualties were feared after an explosion rocked outside Afghan army special forces' base in southwestern Kabul on Thursday, police said.

"At around 12:50 p.m. local time, a blast occurred in front of the gate of Afghan National Army commandos' base in Chahar Asyab district," the police said in a statement.

More details would be made public later as investigation is underway, the statement added.

"We heard a huge blast outside main gate of Afghan National Army Special Operations Corps in Rish Khor locality of Chahar Asyab. The whole place has now been sealed off," an eyewitness told Xinhua.

The blast caused a plume of gray smoke to rise above the scene and the explosion was followed by series of gunfire, he said.

The explosion was the latest in a string of bombings that have targeted dozens of military and security compounds across the country.

No group has claimed responsibility for the attack yet.