Ministers from Hizbollah and its allies resigned today, toppling the Lebanese government of prime minister Saad al-Hariri before expected indictments against the Shi'ite group over the killing of Mr Hariri's father.
Lebanese politicians had said yesterday that Saudi Arabia and Syria failed to reach a deal to contain tensions over the UN-backed tribunal, which is expected to issue draft indictments soon over the 2005 assassination of Rafik al-Hariri.
The ministers resigned as Saad al-Hariri was meeting US president Barack Obama, and the White House later released a statement criticising Hizbollah's moves and warning against any "threats or action" that could destabilise Lebanon.
Mr Hariri's office said he left Washington after the talks, heading for Paris to meet president Nicolas Sarkozy on Thursday.
Analysts said the resignations could set the stage for protracted political turmoil in Lebanon.
They played down prospects of a repeat of the violence of May 2008, when gunmen took over Beirut after government moves against Hizbollah. But Sunni power Saudi Arabia, which backs Hariri, warned the resignations "will cause clashes once again".
The Shi'ite Hizbollah has denied any role in the 2005 killing. Its leader, Sayyed Hassan Nasrallah, has attacked the tribunal as an "Israeli project" and urged Hariri to renounce it. The Sunni Muslim premier has resisted Hizbollah's demand.
Announcing the resignations, Christian government minister Gebran Bassil blamed Washington for obstructing the Saudi-Syrian efforts and called on Lebanon's president to "take the required steps for forming a new government."
A stalemate over the tribunal has crippled Mr Hariri's 14-month-old "unity" government. The cabinet has met, briefly, just once in the last two months and the government could not secure parliamentary approval for the 2010 budget.
A US official said secretary of state Hillary Clinton talked to officials in Egypt, Saudi Arabia and France, seeking backing for the tribunal, adding that US support for it would continue whatever happens to Lebanon's government.
"We also remain committed to working with the government of Lebanon on meeting its own internal security and stability challenges," the official said, dismissing accusations that Washington intervened to scupper Saudi and Syrian efforts.
Lebanon has endured a series of crises since Rafik al-Hariri's killing, including assassinations and the sectarian street fighting in Beirut in 2008, and analysts said the resignations would revive fears of instability.
"You definitely have increased rhetoric, but whether that is matched by a slip towards a bad security situation is not pre-determined," said Karim Makdisi, a teacher of international relations at the American University of Beirut.
Saudi foreign minister Prince Saud al-Faisal urged Hizbollah, which is backed by Iran and Syria, to rejoin the government.
Political scientist Hilal Khashan said Washington had "vetoed" the Saudi-Syrian initiative and there was little prospect of a new government being formed quickly.
The Saudi-Syrian proposals were never spelt out by either country. According to a politician close to Hariri, they would have involved a Hizbollah pledge not to resort to violence if its members were indicted, while Hariri would ensure that any
indictment was not exploited to Hizbollah's political detriment.
Mr Khashan said that while Hizbollah was unlikely to provoke a repeat of the May 2008 violence, he did not rule out protests.
"The phenomenon of food riots is spreading in the Arab world, so the opposition may shield itself behind popular demands for combating inflation," he said.
Reuters