Kabul, Aug 4 : A powerful bomb exploded at on Tuesday evening in the centre of Afghan capital Kabul which was followed by gunshots, the police said. Kabul police spokesman Basir Mujahid said the blast happened at around 8 p.m. at police district 10, adding that more details would be provided after investigations, Xinhua news agency reported. Unknown militants first detonated a car bomb next to the residence of Afghan Defence Minister Bismillah Khan Mohammadi, and the blast was followed by gunshots. According to an eyewitness who refused to be named, after the blast some attackers entered the compound of the minister's house and gunfire continued. The attackers also used hand grenades as some small blasts were heard, people in the area said. Security officials were reluctant to make comments. Fawad Aman, a spokesman for the Defence Ministry, confirmed the defence minister was safe. Eyewitnesses on the condition of anonymity said there were casualties, but with the area cordoned off and gunfire continuing, it was difficult to get more information. /IANS