A Libyan army officer died on Wednesday after a bomb placed in his official vehicle exploded in the restive eastern city of Benghazi, medical and security sources said.

The attack occurred a day after gunmen killed six soldiers at a checkpoint south of Sirte, the hometown of Moamer Kadhafi, highlighting the continuing insecurity in Libya since the 2011 revolution that ousted and killed the long-time dictator.

Lieutenant Colonel Jemaa al-Misrati was "gravely wounded and died of his injuries in the operating room," an official at Benghazi's Al-Jala hospital said.

Witnesses said the bomb exploded shortly after Misrati left home, with a security official saying the vehicle had been "booby trapped".

Eastern Libya, where the 2011 uprising erupted, has seen several attacks against the authorities and Western interests, which have been blamed on Islamists.

Among them was an assault on the US consulate in Benghazi on September 11 last year in which ambassador Chris Stevens and three other Americans were killed.

On Tuesday, unknown gunmen killed six soldiers in a dawn attack on their checkpoint in Khuchum al-Kheil, south of Sirte.

The last bastion of Kadhafi to fall into rebel hands, Sirte has been largely untouched by the wave of violence shaking Libya since the former ruler's regime fell.

Libya's new authorities are battling to establish military and security institutions capable of restoring law and order and state authority in the face of armed militias who fought Kadhafi's forces.