Libya's government has sent troops to put an end to six days of clashes between rival armed groups in the west of the country.
The fighting, which left least 16 people killed and scores of others injured, is the latest episode of instability eight months since the collapse of Muammar Gaddafi's regime after a months-long conflict.
As it seeks to impose its authority on a fractious country, Libya's new leadership on Saturday called for an immediate ceasefire in the fighting south of the capital Tripoli.
The clashes have pitted fighters from the town of Zintan, who played a big role in ending Gaddafi's rule in last year's war, against members of the al-Mashashia tribe, who chose not to join the rebellion, security officials said.
Resentment between the two groups spilled over into fighting in December, when at least four people were killed, and erupted again this week when a Zintan fighter was shot dead.
Zintan's armed groups blamed the Mashashia tribe and retaliated, leading to the current flare-up, which started on Monday, several members of the tribe said.
"The army is going there now to impose a ceasefire and protect civilians," the army's Colonel Hamed Zwei told Reuters news agency.
A security source said heavy fighting continued on Saturday, resulting in many casualties.
"The injured are being taken to hospitals in the area as well as Tripoli; there are so many," he said.
Haramain Mohammed Haramain, one of Libya's three deputy prime ministers, read out a statement to reporters saying the interim government, ruling National Transitional Council (NTC), and religious leaders were all calling for an immediate ceasefire.
Declaring the area a military zone, he said the government had issued instructions to the chief of armed staff and interior ministry to use force if the ceasefire was not respected.
Gaddafi's repressive rule kept in check the deep-running animosities in Libyan society, which often pit villages, cities or tribes against their neighbours.
The flare-ups of violence, mostly in the southern Sahara and mountainous west, raise questions over the ability of the interim government to control the different armed groups.
There are fears that violence in the country may jeopardise a July 7 election for the national assembly.