All five Shia Muslim pro-Syrian ministers in the Lebanese government have resigned, Hezbollah has said.
Hezbollah asked for power of veto at the multi-party talks
They include two Hezbollah members and two from the Amal movement, its ally.
In multi-party talks, Hezbollah had asked for cabinet seats that would give it and its allies power of veto but the majority group in parliament refused.
Lebanese Prime Minister Fouad Siniora said he refused to accept the resignations but the five say they will stick by their decision.
The resignations came just two days before the government was due to discuss a draft UN document on a tribunal for those suspected of killing former Prime Minister Rafik Hariri last year.
The tension in Lebanon has been building since this summer's conflict between Hezbollah and Israel and ahead of the formation of the tribunal.
PM Fouad Siniora says he refuses to accept the resignations
"To pave the way for the majority to practise what it wants freely and so that we don't cover what we are not convinced of... we announce the resignation of our representatives in the current cabinet," said a joint statement by Hezbollah and Amal.
The health minister, Mohammed Jawad Khalifa, one of those who resigned, told the BBC the current cabinet did not reflect recent changes in the Lebanese political landscape.
"What happens when we reach a dead end?" said Mr Khalifa.
"Someone has to take responsibility. Our resignation is a result of not resuming the dialogue. There are no more consultations, and there are differences - so things have come to an end."
The BBC's Kim Ghattas in Beirut says the resignations were something of a surprise as there had been hope that the power-sharing talks would resume at a later date.
The ministers that resigned were in charge of the foreign affairs, agriculture, health, energy and labour portfolios.
More than eight ministers would need to resign for the government to fall.
However, our correspondent says the move could make things very difficult for Western-backed Prime Minister Siniora.
She says Mr Siniora could appoint five different Shia ministers but politically this would add to the growing tension in Lebanon between pro-Syrian groups and the anti-Syrian coalition that has the majority in parliament.
Hezbollah has accused the Lebanese government of failing in its job, and has proclaimed itself the victor of the conflict with Israel earlier this year.