The defence head of a UN-backed special tribunal investigating the murder of former Lebanese prime minister Rafiq Hariri Friday asked judges to lift or suspend arrest warrants against four accused.

"The Defence Office respectfully submits the Chamber should initiate proceedings aimed at lifting or suspending the arrest warrants against the accused," Francois Roux told the Special Tribunal for Lebanon.

The court was mulling Friday a possible trial in absentia of four Hezbollah members accused of killing Hariri and 22 others in a massive car bomb explosion in Beirut on February 14, 2005.

The STL is the only international court that has a mandate to try suspects in absentia and if it does, it would be the first such occurrence since the post-WWII Nazi trials at Nuremberg, said Roux.

So far however, Beirut has failed to arrest the four men wanted for the assassination.

Roux however, said issuing arrest warrants had the opposite effect, "discouraging free and voluntary appearances" by the accused.

The STL was created by a 2007 UN Security Council resolution at Lebanon's request. It opened its doors in 2009, tasked with trying those suspected of responsibility for Hariri's assassination.

It is the first international criminal tribunal with jurisdiction over the crime of terrorism with a mandate to try defendants in absentia.