In a separate incident in the eastern city of Benghazi overnight an explosion injured two members of the special forces.

Gunfire could be heard around 10.00pm (2000 GMT) in the vicinity of the building but it was not clear if it was from the attackers or warning shots from guards inside.

Later in the evening, armed men surrounding the ministry building with sandbags and blocked its entrance with sand, before leaving the area, a security official said.

The official blamed militants from the western city of Zintan of having carried out the attack.

Last Wednesday gunmen from Zintan tried to free five comrades seized by former rebel fighters, a security source told AFP at the time.

At the time the two sides fought it out using small arms and heavy weapons near the centre of Tripoli.