BEIRUT (Reuters) - Ministers from Lebanon's Hezbollah movement and its political allies will resign on Wednesday, forcing the collapse of Prime Minister Saad al-Hariri's government, political sources said.

"The resignation statement has been written and will be announced at 4.30 p.m. (10:30 a.m. ET)," said a senior political source, who asked not to be named. Eleven ministers would quit, enough to automatically bring down the government, he said.

Lebanese politicians on Tuesday said Saudi Arabia and Syria had failed to forge a deal to curb political tensions in Lebanon over a U.N.-backed tribunal set up to try the killers of Hariri's father, former Prime Minister Rafik al-Hariri.

Disagreements over the investigation had paralyzed the "unity" government and revived fears of sectarian conflict.

The tribunal prosecutor is expected to issue draft indictments this month and Hezbollah leader Sayyed Hassan Nasrallah has said he expects members of the group to be accused of involvement.

Hezbollah has denied any role in the 2005 bombing which killed Rafik al-Hariri and 22 others. It has denounced the tribunal as an "Israeli project" and urged Saad al-Hariri to reject its findings -- a demand he has resisted.

Hariri was due to meet U.S. President Barack Obama in Washington around the time of the planned resignation announcement.

Gebran Bassil, a Christian government minister allied to Hezbollah, said Hariri had rejected demands for an urgent session of cabinet to discuss Hezbollah's insistence that Lebanon withdraw all cooperation with the special tribunal.

"The grace period has ended, and the waiting stage that we lived through without any result has ended," he told Reuters.

Hezbollah minister Mohammad Fneish blamed the United States for obstructing attempts by Riyadh and Damascus to find a solution. "There were Arab efforts that gave us the chance to work positively... These efforts have not worked because of American intervention," he said.

Hilal Khashan, professor of political science at the American University in Beirut, said Washington had "vetoed" the Saudi-Syrian initiative and there was little prospect of a new government being formed quickly.

He said Hezbollah was unlikely to repeat the events of May 2008, when gunmen took over Beirut in protest over government steps against the Shi'ite militant movement, but he did not rule out demonstrators taking to the streets.

"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.

Beirut's bourse fell more than 3.0 percent in response to the political turmoil, with shares in market heavyweight Solidere, which has led the reconstruction of Beirut since the 1975-1990 civil war, dropping as much as 7.8 percent.

"(Because) the agreement between Saudi Arabia and Syria was blocked, we have seen a sell-off," said Louis Karam, senior investment adviser at Arab Finance Corporation.

Mochila insert follows.