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BEIRUT, Lebanon (CNN) -- Lebanon's depleted government Monday approved a United Nations draft setting up an international tribunal to try suspects in the assassination of former Prime Minister Rafik Hariri.
The draft laying out plans for a tribunal now goes to the U.N. Security Council.
The decision came amid a deepening political crisis that has introduced questions about the legitimacy of the Lebanese government.
All five Shiite ministers in the 24-member cabinet and one Christian member resigned in advance of the vote. Pro-Syrian leaders argue the remaining 18-member cabinet does not have the authority to make decisions because the Lebanese constitution calls for all sects to be represented in the cabinet.
Anti-Syrian leaders say the resignations were part of an effort to prevent an investigation into Hariri's assassination last year. U.N. investigators have linked Syrian officials with Hariri's killing, but Damascus denies any involvement.
Four of the five Shiite ministers who quit Saturday are part of the Islamic militant group Hezbollah; the fifth, Mohammed Jawad Khalife, is with the Amal political party.
Environment Minister Yaacoub Sarraf, a Greek Orthodox Christian, announced his cabinet exit Monday morning. He is aligned with Lebanon's pro-Syrian President Emile Lahoud.
The remaining 18 members agreed unanimously to the tribunal -- enough for a two-thirds majority that the constitution says is necessary for the government to act.
They made the decision at Monday's three-hour cabinet meeting, which Prime Minister Faoud Siniora convened despite Lahoud's objections.
Saad Hariri -- leader of the top Lebanese parliamentary bloc and son of the slain former prime minister -- was among those who said the ministers' resignations were part of a Syrian-Iranian plot to obstruct formation of a tribunal.
"It's obvious that Iran and Syria has put huge amount of pressure on Hezbollah and Amal not to agree on this matter, and they tried to create a little bit of uncertainty in Lebanon," Hariri said.
"The Syrian regime is responsible for killing Rafik Hariri and all the others, so why protect those who kill Lebanese citizens, Lebanese people, leaders, religious leaders, journalists, members of parliament?" Hariri asked. "I don't understand, and they have to really wake up because the Lebanese people one day will not let them, will not excuse them for their actions."
Hezbollah's Ibrahim Moussawi called for evidence to back up the accusation. "I can accuse you of anything but you have to bring one shred of evidence about the authenticity, the validity."
Khalife, the Amal member who handed in his resignation, told CNN Monday the timing was "a coincidence."
He said the ministers who quit are concerned about forming a national unity government with a "balanced vote." He also cited the need for "a lot of big reforms."
White House Press Secretary Tony Snow said last week that there was mounting evidence that Syria was working with Hezbollah to topple the Lebanese government in an effort to prevent establishment of the tribunal.
Hezbollah has been seeking to control at least a third of the cabinet, enough for veto power.
CNN's Brent Sadler and Nada Husseini contributed to this report.