A Scottish court has begun hearing a new appeal from a former Libyan intelligence agent convicted and imprisoned for the deadly 1988 bombing of a U.S. airliner over Lockerbie, Scotland.

Lawyers for defendant Abdel Basset Ali al-Megrahi based their appeal on a court ruling earlier this year that said a miscarriage of justice may have occurred in the original trial.

Megrahi - a former Libyan intelligence agent - is currently serving a life sentence for his role in the mid-air bombing of Pan Am flight 103 over Lockerbie on December 21, 1988. All 259 people aboard the London to New York flight were killed, along with 11 people on the ground. Megrahi has always denied involvement.

In Thursday's procedural proceedings, defense lawyers asked the court for documents that were unavailable to defense lawyers in the original trial.

The court gave prosecutors six weeks to respond to the request.

The key document relates to the type of timer used to detonate the mid-air bomb. The original jury heard testimony that the bomb's digital timer was manufactured by a Swiss firm that had supplied several of the samples to Libya in the mid 1980s.

But defense lawyers have long argued the timer was a type used by an Iranian-backed militant group in Syria. Defense lawyers have suggested the bombing was an Iranian-financed plot to avenge the shooting down of an Iranian airliner earlier that year by U.S. forces in the Persian Gulf.

Some information for this report was provided by AFP, AP and Reuters.