Colonel Farag al-Dersi played key role in curbing militia power in wake of US ambassador Chris Stevens' murder in September

The Libyan security chief who led an anti-militia crackdown in the wake of the killing of the country's US ambassador has been assassinated in Benghazi, raising questions about the government's ability to impose the rule of law.

Colonel Farag al-Dersi, Benghazi's chief of security, was shot dead by three gunmen in the eastern Libyan city where ambassador Chris Stevens and three fellow diplomats died after the US consulate was overrun on 11 September. The colonel had been instrumental in seeking to curb the power of extremist militias in Benghazi, banning some and trying to bring others under control of government-appointed officers.

His death is the latest in a string of killings and car bombings in the city, most of them targeting officials who had high-profile roles in the former administration of Muammar Gaddafi. To date none of the assassins have been put on trial.

The latest killing highlights the problems faced by Libya's new cabinet, which was sworn-in last week, in tackling the country's security vacuum. Police and army functions remain distributed among a patchwork of militias. Some, notably those in the former key rebel cities of Misrata and Zintan, are well organised, but other parts of the country remain chaotic.

The new government itself is handicapped by the exclusion from office of eight of its 27 ministers, including both interior and justice ministers, by a commission investigating their alleged links to the former Gaddafi regime.

No replacements have been announced by prime minister Ali Zidan, leaving the country still without a full cabinet four months after Libya held its first free national elections in more than 40 years.

The assassination of Dersi also highlights the lack of progress made in catching the killers of Stevens, who died when the consulate was stormed and set ablaze by several dozen militiamen.

Libya has yet to give details of any investigation into the death of what was the first killing of a US ambassador since 1979, or bring any suspects to trial. Also unclear is what role, if any, America's FBI has been given in the case.

The uncertainty at the heart of government is also handicapping reform. A three-day international trade conference meeting this week in the capital, Tripoli, is taking place without the participation of government ministers or officials, leaving investors unsure about Libya's future economic policy, or what plans the government has for establishing security.

 © Guardian News and Media 2012