The Lebanese judge leading investigations into last year's Beirut port blast was forced to stop work Thursday over a lawsuit filed by ex-ministers he had summoned for interrogation, an official said.

The suspension is the fourth since Tarek Bitar was chosen to lead investigations in February.

It comes two weeks since Bitar was cleared to resume work, after a series of court challenges raised by political leaders derailed his efforts.

On Thursday, Bitar was informed of a lawsuit submitted by lawmakers Ghazi Zeaiter and Ali Hasan Khalil -- both members of the Shiite Amal movement -- which forced him to pause the probe until a ruling is issued, a court official told AFP on condition of anonymity.

The total number of lawsuits against Bitar now stands at 18, the official said, most of which were filed by officials he is seeking to interrogate on suspicion of criminal negligence.

Rights groups and relatives of blast victims have repeatedly condemned what they have described as blatant political interference in the investigation.

They say it aims to preserve a culture of political impunity in a country where even assassinations and bombings can go unpunished.

The August 4, 2020 explosion was caused by a huge stockpile of ammonium nitrate fertiliser that was stored haphazardly at Beirut port for years.

Top political and security officials knew of the dangers posed by the shipment but failed to take action.

The powerful Shiite movement Hezbollah is leading demands to remove Bitar.

Its ministers have said they will boycott cabinet sessions until an official decision is taken to replace him.

As a result, the government, which was formed in September to address an unprecedented economic crisis, has failed to meet since October, despite mounting woes.