Grechushkin, a Russian-Cypriot national, was arrested in September at Sofia airport on an Interpol Red Notice [Getty]

The head of Lebanon’s probe into the 2020 Beirut port blast is set to question on Thursday the owner of the ship that carried the ammonium nitrate that ignited the explosion, a Lebanese judicial official has told AFP.

Judge Tarek Bitar is due to arrive in Bulgaria to do this, after the eastern European country denied Beirut’s latest request for the extradition of Igor Grechushkin, the owner of the Rhosus. The application was denied due to insufficient assurances that Lebanon would not apply the death penalty.

Grechushkin, a Russian-Cypriot national, was arrested in September at Sofia airport on an Interpol Red Notice.

He faces charges from Lebanese authorities of “bringing explosives into Lebanon, a terrorist act leading to the death of a large number of people, and disabling machinery in order to sink a ship,” according to the Bulgarian prosecutor’s office.

The Lebanese judicial source who spoke to AFP said he will be questioned in the presence of Bulgarian judicial authorities. They added that Grechushkin’s testimony, including information about the “party that ordered and financed it”, will be used to determine whether Beirut was the ship’s final destination.

Bitar, however, has no power to arrest Grechushkin.

Lebanon’s probe into the causes of the blast and possible negligence by top Lebanese officials has dragged on for years, with families of the explosion’s victims blaming political interference.

The first investigative judge was removed after charging top officials. His successor, Tarek Bitar, also charged senior politicians, who refused questioning, denied wrongdoing and froze his probe.

Bitar resumed his investigation earlier this year and has questioned several officials in recent months but he has yet to issue a long-awaited preliminary indictment.