Three former ministers charged with criminal negligence in connection with the Beirut port blast have asked the Labanon Supreme Court to remove the judge leading the investigation. Nohad Machnouk, a former interior minister and sitting MP, asked the court to replace Judge Tarek Bitar over doubts about his impartiality, the state-run National News Agency reported on Friday. Former ministers Ali Hassan Khalil and Ghazi Zeaiter asked the court to oust Mr Bitar for breaches of the constitution, the NNA reported. Mr Machnouk's request comes weeks after former public works minister Youssef Finianos, who was also charged in connection with the explosion, appealed to the Supreme Court on similar grounds. Mr Machnouk, with Mr Hassan Khalil and Mr Zeaiter, who are both members of Parliament Speaker Nabih Berri’s bloc, had earlier asked the Court of Appeal to dismiss Mr Bitar but their requests were turned down. Mr Bitar replaced Judge Fadi Sawan, who was dismissed by the Supreme Court after Mr Hassan Khalil and Mr Zeaiter questioned his impartiality. All four former ministers, and former prime minister Hassan Diab, who was also indicted in the case, have snubbed Mr Bitar’s summons, arguing that he had no authority to prosecute them under the constitution. Parliament denied Mr Bitar permission to question senior officials in the case, saying they should appear before a special body comprising parliamentarians and senior judges. More than a year after the explosion, it it is still unclear what triggered the explosion of hundreds of tonnes of ammonium nitrate, a chemical fertiliser that was stored at the port for more than six years. Who owned the shipment or why it was left at the port for so long is not clear. The families of victims of the blast, which killed more than 200 people and destroyed large parts of the capital, have accused politicians of stalling and blocking the investigation. Mr Bitar has been the target of criticism from Hezbollah, who accuse the judge of politicising the probe. Media reports tied the explosive chemicals to businessmen close to Syrian President Bashar Al Assad, an ally of Iran-backed Hezbollah. The explosion displaced thousands of people and forced the resignation of Mr Diab’s government, compounding Lebanon’s economic and financial woes.