Thousands of people protested in Libya's two biggest cities on Friday in a show of opposition to moves from some in the oil-producing east to declare autonomy from central rule.
A group of civic leaders in the eastern city of Benghazi this week said they would run their own affairs, defying the government in Tripoli which is already struggling to assert its authority after Muammar Gaddafi was ousted last year.
At Friday prayers in Benghazi and Tripoli, clerics warned the autonomy plan could lead to the break up of Libya, and later crowds packed into squares in both cities to express their opposition to the idea.
"We want to be one country," said 18-year-old Taha, one of about 5,000 people taking part in the demonstration in Tripoli's Martyr's Square. "This is what we fought for ... We are going to stand as one man and say no to federalism."
In Benghazi's Tahrir square, between 3,000 and 4,000 people joined in the protest against the autonomy plan, which aims to recreate Libya's 1950s constitution when the country was divided into three semi-autonomous provinces.
The protests were some of the biggest in Libya in several months.
Earlier, a cleric addressing about 1,000 worshippers praying on mats laid out in Benghazi's Tahrir square, called on people to resist the push for autonomy.
"We should keep Libya as one country, one family," said the cleric. "Federalism will take Libya backwards because it will split the country."
Civic leaders in Benghazi on Tuesday declared the creation of a "Provincial Council" to run the affairs of Cyrenaica, the historic province which runs from the border with Egypt in the east to half way across Libya's Mediterranean coast.
The province is home to Libya's biggest oil fields, and the new council, if it can assert real power, could cause complications for international oil firms. They might have to re-negotiate their contracts with the new provincial entity, as well as with Tripoli.
Cyrenaica flourished in the 1950s when it enjoyed the patronage of Libya's royal family. But after Gaddafi came to power in a 1969 coup the province fell into decay and was denied its share of the country's oil wealth.
After the rebellion which forced out Gaddafi, many in the east expected an immediate injection of money and development. They have been frustrated at the slow pace of change coming from the interim government in Tripoli.
Yet even in the east, there is no consensus in favour of the plan for autonomy.
"We are against the idea of a federal system and we will protect Libyan unity with our lives," said Hakim Abdulrahman Hamad, head of the city council in the eastern city of Tobruk.
"We support freedom for the Libyan people but not to split the country up," he told Reuters. "The choice about the type of government should be taken by parliament, through democratic means."