Lebanon's President Michel Aoun on Tuesday warned politicians not to interfere with the investigation into the Beirut port blast.
A campaign to remove the lead investigative judge has gained ground, paralysing political life and reviving sectarian tensions.
The Iran-backed Hezbollah group and its allies have stepped up efforts to remove Tarek Bitar from the probe after a protest they organised against him ended in bloodshed last week.
“President Aoun stressed the independence of the judiciary with regard to the ongoing investigations into the Beirut port explosion, and the need for politicians not to interfere in the probe,” the presidency's Twitter account said.
The investigation into the causes of the Beirut blast, which killed more than 215 people last year and injured more than 7,000 others, has stalled under political pressure. One lead judge has already been removed.
Victims and activists have accused politicians of seeking to torpedo the probe to evade justice, waving the threat of renewed civil strife to justify impunity.
“This concerted campaign against Judge Bitar has escalated to the point of suggesting that if he remains in his role, this would sow discord and start a civil war,” said Ghida Frangieh of Justice watchdog Legal Agenda.
She described political efforts to undermine the probe as an “unprecedented” attack on the independence of justice in Lebanon, at a press conference on Tuesday to support Mr Bitar.
Families of the victims called on politicians to stop interfering in the probe.
Mr Aoun is an ally of Hezbollah and a staunch rival of the Christian Lebanese Forces, whom Hezbollah accuses of shooting dead seven of its supporters during a protest calling for Mr Bitar's removal.
The LF claimed supporters had taunted residents because they marched into a Christian district shouting sectarian slogans. Unverified video footage of a soldier shooting at a protester has surfaced and the army said it was investigating the incident. A military court later summoned LF leader Samir Geagea to give a statement on the deadly gunfights.
Mr Geagea, the leader of the country's second largest Christian party, said he would appear for a hearing only if investigators listen to Hezbollah leader Hassan Nasrallah first. The LF also accused Hezbollah of seeking to derail the Beirut blast probe.
Lebanon’s leading Christian cleric, Patriarch Bechara Rai, condemned the summons against Mr Geagea and stressed the importance of a “free and independent” judiciary after a meeting Parliament Speaker Nabih Berri, Hezbollah's Shiite ally.
Discussions touched on the Cabinet paralysis and its impact on the economy, the patriarch said. The Cabinet has yet to meet after ministers affiliated with Hezbollah and its allies threatened to boycott the coming session if Mr Bitar was not replaced. Later in the day, the patriarch met Mr Mikati.
Sunni leader and former prime minister Saad Hariri also sided with Mr Geagea on Tuesday, describing the summoning as “absurd,” and saying it would stir up sectarian divisions.
Many of the politicians summoned for interrogation by Mr Bitar are aligned with Hezbollah and its Shiite ally, Mr Berri. Both led the campaign for Mr Bitar’s removal after he issued arrest warrants for two former ministers including an aide to Mr Berri and a member of his parliamentary bloc.
Former prime minister Hassan Diab and sitting parliamentarians and former ministers Nohad Machnouk and Ghazi Zeaiter are scheduled to appear for interrogation before Mr Bitar this week.
Mr Zeaiter and Mr Machnouk had previously asked for the removal of Mr Bitar from his post.
Politicians who had been summoned for questioning by Mr Bitar’s predecessor succeeded in removing the judge investigating them in February.
Reema al Zahed of the Beirut Blast Victims Families' Association, called on authorities to stop interfering in Mr Bitar's work.
“Our deliverance is a transparent judiciary far away from political agendas and the games you play,” she said during the conference.