BEIRUT- A probe into the catastrophic explosion at Beirut port was frozen on Monday when a former minister wanted for questioning as a suspect filed a case questioning the lead investigator's neutrality, a judicial source said.

The Aug. 4, 2020 Beirut port blast killed more than 200 people, injured thousands and destroyed swathes of Beirut. It was caused by a large quantity of explosive chemicals stored at a warehouse unsafely for years.

The judicial probe into the explosion, one of the biggest non-nuclear blasts ever recorded, has made no progress, angering many Lebanese including families of the victims who are furious that no senior officials have been held to account.

Judge Tarek Bitar was appointed lead investigator after the removal of his predecessor in February on similar grounds.

Bitar was notified on Monday of the case against him filed by former interior minister and current member of parliament Nohad Machnouk, the judicial source told Reuters.

"Now the sessions will be cancelled and Judge Bitar will stop looking at the file until the court of cassation decides either to accept the case or reject it," the source said.

There was no immediate comment from Bitar, who is not permitted to speak to the media.

The probe has faced political pushback from powerful parties that have alleged bias in the investigation.

The court of cassation issued a decision in February that removed the first judge, Fadi Sawan, from the case after a request from two former ministers he had charged, Ali Hassan Khalil and Ghazi Zeaiter.

Judge Bitar had issued requests in July to question former prime minister Hassan Diab and other top officials charged by his predecessor with negligence over the blast.

All have denied wrongdoing.

On Sept. 16, he issued an arrest warrant for former public works minister Youssef Finianos after he failed to show up for questioning, the first against a top official in the case.

(Reporting By Laila Bassam and Maha El Dahan; Editing by Jon Boyle/Tom Perry/David Evans) ((Maha.Dahan@thomsonreuters.com; + 9712 4082101; Reuters Messaging: maha.dahan.thomsonreuters.com@reuters.net))