The headquarters of the public prosecutor in Benghazi that was targeted

An improvised bomb exploded outside the headquarters of the public prosecutor in the Libyan city of Benghazi causing material damage but no fatalities, a security source has said.

"Initial evidence suggests the device was a suitcase packed with high yield explosives (TNT)," an investigator at the scene said, adding that there were no casualties.

The overnight blast marked the third attack on the site in 2012, he reportedly told News 24

It damaged the front of the recently renovated building, which once held the people's court, a special tribunal created by the former dictatorial Muammar Gaddafi regime to crack down on opponents, particularly Islamists.

The bomb also punched a hole in the ground and shattered the glass of adjacent vehicles and properties.

December marked a tumultuous month for Benghazi, cradle of the 2011 uprising that toppled the Gaddafi regime and ended in his killing.

A spate of attacks targeting police stations claimed the lives of seven officers in December and pushed the chief of staff to send reinforcements to bolster security there.

In 2012, Libya's second city witnessed a series of assassinations targeting security officials and judges, many of whom had served under the previous regime.

Benghazi has also emerged as a hub for jihadist groups, including militants who killed ambassador Chris Stevens and three other Americans in a 11 September attack on the US consulate.