Saudi Arabia and Syria have failed to broker a deal to curb tensions in Lebanon over an international investigation into the 2005 killing of former premier Rafik Al-Hariri, Lebanese politicians said on Tuesday.

The apparent breakdown prompted calls from Hezbollah and its allies for an urgent cabinet meeting, and one source said they would pull out of the government unless it agreed to halt co-operation with the UN-backed tribunal.

The two Arab states, who back rival camps in Lebanon, have worked since July to overcome deep disagreements over the tribunal which have paralyzed Lebanon's government and revived fears of sectarian conflict.

'This initiative has ended without a result,' said Michel Aoun, a Christian leader and political ally of Hezbollah, which expects some of its members to be named in indictments due to be  issued soon by the tribunal prosecutor.

Hezbollah has denied any involvement in the 2005 bombing which killed Hariri and 22 others. It has denounced the tribunal as an 'Israeli project' and urged Prime Minister Saad al-Hariri -- son of the slain Sunni leader -- to reject its findings.

Okab Sakr, a Shi'ite politician close to Hariri, said there had been no statement from Saudi Arabia or Syria on the status of their initiative, and that Hariri and President Michel Suleiman would continue efforts 'to solve the crisis.'

A source in the Hezbollah-led group which forms part of the fragile unity government, speaking after Aoun's announcement, said the Shi'ite movement and its allies were demanding that cabinet meet and halt Lebanon's co-operation with the tribunal.

'If these decisions are not taken, we will withdraw from the government,' the source said.

Hezbollah and its allies would need one more minister to pull out of the cabinet in order to topple the government.-Reuters