|Hezbollah wants Lebanon to end its co-operation with the UN investigation in Rafiq al-Hariri's assassination [AFP]
Hassan Nasrallah, Hezbollah's leader, has said his party will refuse to back Saad Hariri, Lebanon's caretaker prime minister, in forming a new government.
Nasrallah's comments, broadcast on Al-Manar television on Sunday, were his first public comments since Hezbollah ministers and their allies pulled out of Lebanon's government causing it to collapse.
Hezbollah, which has a political bloc in parliament as well as a powerful military wing, commands strong support in Lebanon's Shia Muslim community.
"The opposition unanimously will not name Hariri tomorrow," Nasrallah said, calling his party's move to bring down the government "constitutional, legal and democratic".
Lebanon's crisis is the result of long-simmering tensions over the UN tribunal that is investigating the 2005 assassination of Rafiq al-Hariri, a former Lebanese prime minister and the father of Saad Hariri.
The tribunal is widely expected to indict members of Hezbollah, which many fear could rekindle violence in Lebanon.
"Despite the fact we reject the indictment simply for being politicised, Lebanon is our homeland and we are keen on its safety and stability," Nasrallah said in his speech.
Hezbollah has several times denounced the Netherlands-based tribunal as a conspiracy by the US and Israel.
The group demanded that Saad Hariri's government reject the court's findings even before they come out.
But though he offered some concessions, Saad Hariri has refused to end co-operation with the tribunal, prompting Hezbollah's walkout.
The US earlier denounced Hezbollah's move as an attempt to evade justice.
"The tribunal is an independent, international judicial process whose work is not subject to political influence, either from inside Lebanon or from outside," Maura Connelly, the US ambassador to Lebanon, said on Sunday.
"The efforts by the Hezbollah-led coalition to collapse the Lebanese government only demonstrate their own fear and determination to undermine Lebanon's sovereignty and independence."
Michel Sleiman, Lebanon's president, has asked Saad Hariri to stay on as a caretaker leader and consultations on the appointment of a new prime minister are due to take place on Monday.
Rula Amin, Al Jazeera's correspondent in Beirut, said that a new government might be formed relatively quickly.
"It could be a very quick process, that's what the opposition want - they want a new government that will do what Mr Hariri was not willing to do, which is to end Lebanon's co-operation with the tribunal," she said.
"However, they are still not sure if they will have enough members of parliament who would support such a move."
Lebanon's crisis has sparked fears in the region.
Sheikh Hamad bin Khalifa Al-Thani, the Qatari emir, and Recep Tayyip Erdogan, the Turkish prime minister, are due to meet Bashar al-Assad, the Syrian president, in Damascus on Monday to discuss the situation.