BENGHAZI, Libya (AFP) - Fierce clashes broke out on Monday between army special forces and fighters from Libya's top jihadist group in the eastern city of Benghazi, killing at least five soldiers, officials said.

The army declared a "state of alert" and ordered all soldiers to report for duty at barracks.

"A violent clash has been taking place for several hours between our forces and an Ansar al-Sharia cell," Colonel Milud al-Zwei, spokesman for Libya's special forces, told AFP.

Updating an earlier toll, medics at the city's Al-Jala hospital, said five soldiers were killed and 23 people wounded, including 10 civilians.

Col Zwei said the fighting - the first of its kind between the army and the Salafist group - broke out after a special forces patrol near the group's headquarters came under attack.

"The army retaliated, sparking clashes with all types of weapons," he said.

The spokesman said fighting between the two sides spread to other districts of Benghazi, especially near a charity clinic run by Ansar al-Sharia in the Selmani area.

Ansar Al-Sharia emerged after the 2011 fall of Muammar Gaddafi's regime, with its military wing composed of former rebel fighters.

Blamed for the murders of judges and members of the security forces in Benghazi, it is also suspected of responsibility for a September 2012 attack in which the US ambassador and three other Americans were killed.

It denies any involvement.