TRIPOLI: The trial of Libya's former spy chief Bouzid Dorda was adjourned for a fourth time Tuesday as defence lawyers challenged the legality of proceedings in the first case against a top Moamer Kadhafi official.

"We have appealed to the Constitutional Court over the illegality of the procedure by which our client was brought before the court," said defence counsel Ali Mohammed al-Dhabaa.

"We want to wait for the Consitutional Court's ruling."

A new hearing was set for September 11. It was the fourth adjournment since the trial opened on June 5.

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 Kadhafi'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.