Thousands of Libyans have rallied in the country's two main cities to denounce moves by leaders in the east to create a semi-autonomous territory.
Demonstrators chanted slogans demanding unity and used shoes to hit photos of Ahmed Zubair al-Senussi, the head of the regional council seeking a split.
The rallies took place after Friday prayers in the capital Tripoli and in Benghazi, the main city in the east.
Tribal and militia leaders there announced the move on Tuesday.
In a BBC interview, Mr Senussi said he was ready to hold talks with the country's leadership about setting up the oil-rich semi-autonomous territory, to be known as Cyrenaica.
He said he was committed to federalism but was prepared to discuss what form it would take.
In a speech on national TV on Wednesday, interim leader Mustafa Abdel Jalil, of the National Transitional Council (NTC), also called for dialogue but said national unity would be defended by force if necessary.
Crowds gathered in central areas of both cities after clerics at Friday prayers warned that the autonomy plan could lead to the break-up of the country.
In Tripoli, Martyrs' Square was the focal point of demonstrations, with people chanting "No, no to federalism" and "Libya is one".
Correspondents say the declaration has significant popular support among people in Benghazi, but there is no consensus despite frustration with the slowness of change since the overthrow of longtime leader Col Muammar Gaddafi last year.
Following independence in 1951, Libya's three regions enjoyed federal power until the country became a unitary state in 1963.
Cyrenaica stretches from the central coastal city of Sirte to the Libyan-Egyptian border in the east. It contains two-thirds of the country's oil reserves.
The people of Cyrenaica, known as Barqa in Arabic, felt particularly marginalised and neglected under Gaddafi, who focused much of the development on the west, correspondents say.
The city of Benghazi was the seat of the uprising that eventually toppled the former dictator, in August last year.
The autonomy plan calls for a regional parliament and control over the police force and courts, but stops short of advocating a division of the country.