A Lebanese judge leading the investigation into last year’s massive explosion at Beirut’s port issued a subpoena for the country's caretaker prime minister after he failed show up for questioning on Thursday, the state-run National News Agency reported.

Last month, judge Tarek Bitar confirmed charges filed by his predecessor against outgoing Prime Minister Hassan Diab and three former ministers. Dian was summoned for questioning on accusations of intentional killings and negligence. Bitar also summoned former and current generals.

Hundreds of tons of ammonium nitrate, a highly explosive material used in fertilizers that had been improperly stored in the port for years, exploded on Aug. 4, 2020, killing 214 people, injuring more than 6,000 and devastating nearby neighborhoods.

The blast was one of the largest non-nuclear explosions ever recorded and was the most destructive single incident in Lebanon’s troubled history. Bitar set a new date for questioning Diab, Sept. 20.

The prime minister had also declined to be interrogated last year by Bitar's predecessor, Fadi Sawwan. Bitar was named to lead the investigation in February after Sawwan was removed following legal challenges by senior officials he had accused of negligence that led to the blast.

Diab, who resigned following the explosion, said in an interview last year with The Associated Press that he was being singled out and charged while others knew more.

On Wednesday, Bitar supervised a simulation of the welding that took place at the port shortly before last year's explosion, according to the news agency's report. Its aim was to determine whether the welding could have been the main cause of the fire that preceded the explosion. The simulation was attended by a group of lawyers and security officers.