image source, EPAimage captionVictims' relatives showed their support for Tarek Bitar at a demonstration in Beirut last week

The Lebanese investigation into the devastating blast in Beirut last year has been suspended after an ex-minister wanted for questioning complained about the lead judge's impartiality.

Judicial sources said Tarek Bitar would stop the probe until a court had ruled on Nohad Machnouk's case.

Judge Bitar has been struggling to get high-profile witnesses to testify.

His predecessor was removed on similar grounds in February after he accused former ministers of negligence.

The massive explosion at Beirut's port on 4 August 2020 killed at least 218 people, wounded 7,000 others and devastated swathes of the city.

A fire triggered the detonation of 2,750 tonnes of ammonium nitrate, a combustible chemical, that had been stored unsafely in a warehouse for almost six years.

The disaster compounded a deep economic crisis in Lebanon that has pushed three quarters of the population into poverty.

media captionOne year on from the Beirut blast

The ammonium nitrate arrived at the port in 2013, when a Moldovan-flagged cargo vessel made an unscheduled stop there and was then banned from leaving because of a legal dispute over unpaid fees and ship defects.

In 2014, the ship was deemed unseaworthy and its cargo was unloaded to a port warehouse following a court order.

The heads of the port and customs authority said their warnings about the danger posed by the ammonium nitrate and calls for it to be removed were repeatedly ignored.

More than 20 people, most of them port and customs officials, have so far been arrested as part of the investigation into the explosion.

The first lead judge, Fadi Sawan, decided last December to charge the prime minster at the time of the incident, Hassan Diab, and three other former senior officials – ex-finance minister Ali Hassan Khalil and ex-public works ministers Youssef Finyanus and Ghazi Zaiter – with negligence.

They denied any wrongdoing and refused to be questioned as suspects, accusing the judge of overstepping his powers.

Judge Sawan was removed from the case by the Court of Cassation in February in response to complaints from Mr Khalil and Mr Zaiter. The decision was based in part on the fact that the judge's home was damaged by the port blast, which the court said raised questions about his impartiality.

His replacement, Judge Bitar, has also sought to question the four men, as well as Mr Machnouk, a former interior minister, and several former army and security chiefs.

More on the explosion in Beirut

  • The ship of ‘lost lives and dreams’
  • The inferno and the mystery ship
  • Beirut explosion: Before-and-after images

Earlier this month, he issued an arrest warrant for Mr Finyanus after he failed to appear before him. That prompted the former minister to request the judge's removal by the Court of Cassation, alleging "legitimate suspicion" of bias over his handling of the case.

But it was not until Mr Machnouk made a similar complaint last week that the judge's investigation was paused, to the intense disappointment and frustration of the victims' families, who are desperate for answers.

"There is great anger among the families. There is a type of disgust towards the political class," said Ibrahim Hoteit, whose brother was killed in the blast.

Mr Diab, who was recently replaced as prime minister by Najib Mikati, has flown to the United States. An adviser has said he is visiting his children there and that he can only be summoned for questioning if parliament approves.