Lebanese Prime Minister Fouad Siniora has accused the leader of the Hezbollah militant movement of plotting a coup.
Siniora's government is under severe pressure
He pointed to comments by Hezbollah's Hassan Nasrallah that the opposition would form an interim government without the existing administration.
Mr Siniora said these were tantamount to a plot to overthrow the government.
In another development, a Sunni preacher led thousands of Sunni and Shia anti-government protesters in a show of unity during Friday prayers.
The preacher, Fathi Yakan, praised the protesters for trying to stop what he called the American project in Lebanon - a reference to western support for Mr Siniora's government.
Speaking in al-Jazeera TV, Mr Siniora said: "The least that can be said is that Mr Nasrallah was not right yesterday to say what he said."
"He is trying to stage a coup. Or at least he's threatening to stage a coup. And he has already decided the outcome."
In a televised address on Thursday, Sheikh Hassan Nasrallah also said street protests would continue until the opposition achieved its aim of forming a new national unity government.
Sheikh Nasrallah told supporters camped in central Beirut that Lebanon needed a new government, one free from foreign influence.
He said Hezbollah was open to negotiations, and would not fight fellow Lebanese.
The group, backed by Iran and Syria, withdrew from government last month.
Thousands of Hezbollah followers have been protesting in central Beirut for a week, with sporadic clashes between government and anti-government supporters.
Hezbollah withdrew its minister from the government last month - and other pro-Syrian members of the cabinet followed suit.