Saad Hariri, the Lebanese prime minister, is in Washington for talks with Barack Obama, the US president [EPA]

Lebanon's unity government looks close to collapsing after the Hezbollah movement and its political allies threatened to walk out over arguments stemming from a UN probe into the assassination of Rafiq al-Hariri, the former Lebanese premier, in 2005.

There has been growing political tension in Lebanon, amid signs that Hezbollah members could be indicted by the UN-backed Special Tribunal for Lebanon (STL).

Eleven ministers had said they would tender their resignations on Wednesday unless a cabinet meeting was convened to discuss the investigation by the STL.

Ministers allied to Hezbollah told local media that Hariri had rejected the call for a cabinet session, which was requested on Tuesday after officials announced that a diplomatic push by Syria and Saudi Arabia to ease political tensions in Lebanon had failed.

The move came as al-Hariri's son Saad, the current prime minister, was in Washington to meet Barack Obama, the US president.

Hezbollah, which has denied any role in the assassination, has denounced the tribunal as an "Israeli project'' and urged Hariri to reject any findings by the court, which has not yet announced its decisions.

But the prime minister has refused to break co-operation with the tribunal.

Al Jazeera's Rula Amin, reporting from Beirut, said: "They [the ministers] will submit their resignation this afternoon at just about the same time that Saad al-Hariri, the prime minister, will be meeting with Barack Obama, the US president," she said.

"So Obama will probably be meeting him as the former prime minister and not as the current prime minister."

Failed talks

"This [threat of resignations] comes after reports that the Saudi-Syrian efforts to try and broker a deal between the different Lebanese factions over the international tribunal had failed," said Amin.

"Now the opposition here, led by Hezbollah, are blaming the US. They said the US administration had put all its efforts into sabotaging this initiative - they did not want to get Hezbollah off the hook."

Syria and Saudi Arabia have for months been attempting to act as mediators in the crisis but their efforts have failed with each side accusing the other of refusing to compromise.

"Saad Hariri was on the brink of making a major concession as concerns the tribunal but occult forces prevented him from doing so," Walid Jumblatt, the Druze leader, told the AFP news agency without elaborating.

The standoff between Hariri's camp and Hezbollah over the UN tribunal has paralysed the government for months and sparked concerns of sectarian violence similar to the one that brought the country close to civil war in May 2008.

Source: Al Jazeera and agencies