The trial of Libya's former spy chief Bouzid Dorda was adjourned indefinitely on Tuesday as defence lawyers challenged the legality of proceedings in the first case against a top Gaddafi official.

It was the fifth time since 5 June that the trial had been suspended at the request of defence lawyers.

"It was decided that the trial would be suspended until the Constitutional Court gives its verdict on the defence application," the judge said.

The defence says it rejects the "illegality of the procedure" by which Dorda was brought before the court.

On 28 August, defence lawyers made a similar application, after which the trial was adjourned until Tuesday.

The former foreign intelligence chief is accused of ordering security forces to use live ammunition against demonstrators last year.

He faces five other charges, including detaining people without evidence of any crime and organising members of his tribe into an armed militia with the aim of sparking a civil war.

His is the first public trial of a senior Libyan official accused of killing demonstrators in the 2011 uprising that ended Muammar Gaddafi's rule.

Dorda served as Libya's UN envoy in the late 1990s and replaced Mussa Kussa as head of external intelligence services in 2009 before he was detained in September last year.

The new Libyan authorities have been keen to show the world they have a strong judiciary and are capable of conducting fair trials for high-profile figures.