Journalists in post-revolution Libya face the constant threat of attack and have lost even the limited freedom that existed under slain strongman Moammar Gadhafi, Human Rights Watch said on Monday.

A 54-page report by the New York-based rights watchdog released in Tunisia said journalists in Libya are "assaulted, kidnapped and killed with impunity".

A suicide car bomber struck a Libyan army post in the battleground second city of Benghazi on Friday, killing a father and son, the military said.

Milud al-Zwei, spokesman for the army's special forces, said the blast killed the two bystanders and wounded 20 other people, mostly soldiers.

The Islamic State group is gaining ground in Libya and a new international approach is needed to address the growing threat, a senior Libyan official said Thursday.

Aref Ali Nayed, Libya's ambassador to the United Arab Emirates and an adviser to Prime Minister Abdullah al-Thani, was in Washington and New York this week to discuss the new challenges on Libya's security front.

Gunmen in Libya killed 13 people, including five foreigners, in an overnight attack on a oil field partially owned by France's Total, a chief security officer said on Wednesday.

"Eight Libyans, three Filipinos and two Ghanians were killed in the attack" at the al-Mabruk field, said officer Hakim Maazzab, the head security guard at a nearby oil complex.

Sixteen Libyan soldiers were killed and 38 wounded in clashes around an eastern Islamist stronghold and close to a key oil terminal, military officials said Tuesday.

"The army lost 11 soldiers... in violent clashes with radical Islamists after an army offensive launched on Monday" near the town of Derna, said Colonel Ahmed al-Mashari.

Libya's internationally recognized parliament on Monday voted to suspend a controversial law that barred officials from the era of toppled strongman Moammar Gadhafi from holding political posts.

"The House of Representatives voted in favor of suspending the law of political exclusion until the adoption of a permanent constitution," lawmaker Tarek al-Jerushi said, adding that the law could now be considered "annulled."

A car bomb exploded Monday near the Tripoli headquarters of a Libya militia which controls the capital, killing one person and wounding two others, a security source said.

The attack targeted the Tripoli Revolutionaries Brigade militia which occupies a former security building near the center of the capital, said the source.

A senior oil official who represents Libya in the OPEC cartel has been freed after being kidnapped last month in Tripoli, National Oil Company sources said Monday.

Samir Salim Kamal, an NOC engineer who is also Libya's governor for the Organization of Petroleum Exporting Countries, had not been seen since January 15 when he left the company's offices.

The rivals of Libya's elected parliament agreed Thursday to join U.N.-mediated peace talks with the internationally recognized government if they are held on home soil.

The announcement by Salah al-Makhzoum, deputy speaker of the General National Congress (GNC), came as the United Nations said there was agreement in principle to hold future sessions in Libya, "provided that logistical and security conditions are available."

Ending conflict in Libya can only be achieved through a political deal, Libyan and regional leaders said Wednesday after African Union-led talks.

"The only solution to bring an end to the current crisis in Libya is a political settlement," Libyan Foreign Minister Mohamed Dayri said after meeting with the AU's International Contact Group for Libya, ahead of a summit Friday of the continent's leaders in the 54-nation bloc.