Hezbollah and its allies are threatening to quit the Lebanese government this afternoon – a move that would likely end prime minister Saad Hariri’s reign and destabilise the fragile state.Hezbollah lawmakers have said they will abandon the coalition after months of fruitless wrangling over how to deal with criminal indictments likely to accuse group members of being behind the assassination of former prime minister Rafiq Hariri in February 2005.The health minister, Mohammed Jawad Khalifeh, told Hezbollah’s al-Manar TV that ministers would resign unless Saad Hariri – Rafiq’s son – agreed to convene an urgent cabinet meeting.The threat follows months of tension in Lebanon that has threatened to split the country on sectarian lines. Several regional initiatives have attempted to broker face-saving deals for both Hezbollah and Hariri’s political bloc, which forms the majority of the coalition.At issue is the work of the UN-backed special tribunal for Lebanon, which has been investigating his father’s death and that of 11 others who supported his bloc or opposed Syrian influence in Lebanon.Hezbollah’s threat is being perceived as brinkmanship by some members of Hariri’s bloc, who say the former has too much to lose by walking away. Lebanon’s cabinet has not made a decision in the past three months as both sides remained at odds over the tribunal.Saudi Arabia and Syria have taken a lead in one initiative, the full details of which have not been made public. However, it is known that Hezbollah expects Hariri to disavow the tribunal’s findings, which would make it difficult for those named in the indictments to be prosecuted.Hezbollah’s threat is being seen as an attempt to spoil today’s planned meeting between Hariri and Barack Obama at the White House. Obama has taken an active role in attempting to defuse the Lebanon tensions, which both he and the US secretary of state, Hillary Clinton, have said could spark a broader sectarian flare-up in the Middle East.The US has insisted on the tribunal delivering its findings, and on the prosecution of those indicted. It would be a serious blow to Hezbollah, which casts itself as a nationalistic group whose militant acts against Israel, including a devastating war in July 2006, have been carried out in Lebanon’s name.Hezbollah’s opponents have long viewed it as acting largely in the interests of its two regional backers, Iran and Syria, both of which are often at odds with the Sunni Muslim world, especially Saudi Arabia and Egypt.Hezbollah has for the past three months sustained a heated campaign against the UN tribunal, saying it was picked by conspirators acting on behalf of the US and Israel.The tribunal had earlier in the investigation alleged that Syria was behind the killing of Rafiq Hariri and has not retracted this despite the upcoming indictments. It identified 10 mobile phone numbers used by the team that carried out the bombing outside the St George hotel on Beirut’s waterfront. The identities of the people who used the phones had not been established, it said.In 2007 a Lebanese investigator, Wissam Eid, discovered evidence linking some ranking members of Hezbollah to the phones. Eid was killed several months later by a car bomb near his office. The indictments are widely believed to hinge on his work.• This article was amended on 14 and 18 January 2011. Owing to an editing error, it referred to the assassination of “then prime minister Rafiq Hariri in February 2005”. Hariri resigned the previous October and Omar Karami was prime minister when Hariri was assassinated. This has been corrected.