BEIRUT, Lebanon —  A weakened Lebanese government on Monday approved a U.N. plan for an international tribunal for suspects in the assassination of former Prime Minister Rafik Hariri _ despite the resignation of six ministers and the objections of the president.

The vote was a victory for Prime Minister Fuad Saniora, who is facing a Hezbollah threat of mass protests unless the group and its Shiite Muslim allies gain effective veto power in the Cabinet. All 18 ministers remaining in the Cabinet voted for the U.N. plan, which begins the process of prosecuting Hariri's alleged killers in a court with international legitimacy.

The draft document now returns to the Security Council for endorsement, but its final approval by the weakened government was far from certain.

"Our aim is to achieve justice and only justice,"Saniora said after the three-hour Cabinet meeting.

Hariri was killed with 22 others in a suicide truck bombing in February 2005. The assassination sparked huge protests against Syria, which was widely seen as culpable. Syria denied involvement, but was forced to withdraw its troops from Lebanon, ending a 29-year domination of the neighboring country. Subsequent elections produced an anti-Syrian majority in parliament and in the Cabinet.

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However, some opposition figures said the Cabinet's approval was illegal because none of the five Shiite ministers who resigned Saturday was present.

Pro-Syrian President Emile Lahoud said Sunday that Saniora's government was no longer legitimate because the constitution requires that"all sects should be justly represented in the Cabinet."The constitution recognizes 18 religion-based communities and most of them are represented in a full Cabinet by at least one minister. Half the ministers have to be Christian and half Muslim.

Lahoud said all decisions taken by the Cabinet, including Monday's, were"null and void."

Michel Aoun, the leader of a Christian faction allied with Hezbollah, agreed.

"The government has lost its legitimacy and its decision today to approve the draft document ... is meaningless."

Environment Minister Yaacoub Sarraf, a Christian minister allied with the president, resigned shortly before the Cabinet meeting, citing similar objections.

"I don't see myself belonging to any constitutional authority in which an entire sect is absent,"Sarraf wrote in his letter of resignation.

Saniora refused to accept Sarraf's resignation, as he had refused to accept those of the Hezbollah and Shiite Amal ministers on Saturday.

In Washington, State Department spokesman Sean McCormack said the root of the tension was fear of what may emerge in the tribunal.

"It's very clear that there are some (people), outside of Lebanon as well as inside of Lebanon, who don't want to see passage of this tribunal because, either they, themselves, are worried that they may end up before such a tribunal, or that their friends will end up before such a tribunal,"McCormack told reporters.

The anti-Syrian camp in Lebanon has charged that Syria is behind the opposition to the tribunal because it seeks to avoid the prosecution of the Syrians implicated in Hariri's killing by a U.N. inquiry. Hezbollah officials have denied they are opposed to a U.N. tribunal and Aoun called the accusation"a lie."

Saniora insisted the Cabinet's move was legal. His Information Minister Ghazi Aridi extended a hand to opponents, saying the government was willing discuss their grievances.

"We have no choice but dialogue to agree on all the issues,"Aridi said.

Saniora still has the necessary two-thirds of the 24-member Cabinet in order to hold meetings and make decisions, but he will find it difficult to govern as passing legislation depends on forging alliances among the many factions in parliament.

The U.N. proposals seek to create a"tribunal with an international character,"but Lahoud has criticized the presence of foreign judges and said he would not pass an earlier draft.

Once the Security Council has endorsed the final draft, it must be approved by Lebanon's Cabinet again, signed by the president and approved by parliament.

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