Four years after the attack at Sarafovo airport in the Black Sea city of Burgas, the trial for the death of five Israeli tourists and a Bulgarian bus driver has again been adjourned by the Specialized Criminal Court.

The reason cited are procedural irregularities in the summoning of witnesses, including people who were left wounded in the attack.

Separately, the court had failed to inform the victims' relatives the trial was beginning.

A new sitting has been scheduled for November 10.

Two people, one (named Meliad Farah) with dual Australian-Lebanese citizenship and another (El Hajj Hassan) with Canadian-Lebanese citizenship, have been indicted in absentia after not being sought through Interpol for months.

The prosecution alleges they helped suicide bomber Mohamad Hassan El Husseini detonate an explosive device in the parking area in front of the arrivals of the airport in on July 18, 2012.

They supposedly provided assistance to El Husseini between June 28 and July 11.

The two defendants face life imprisonment if convicted.

Thirty-five other Israeli tourists were injured in the suicide blast, alongside their Bulgarian guide. The tourists were en route to their hotel in the resort of Slanchev Bryag, where a bus was to take them from the airport.

There are 80 volumes of court material, 170 witnesses and 100 expertises as part of the trial.