Libyan authorities on Saturday declared warring mountain towns in the west of the country a "military zone" and called for an immediate ceasefire.
"As a result of the violence in the areas of Mizdah, Sheguiga and Zintan which has killed innocent people, the interim government... orders all parties to immediately stop their fire," Prime Minister Abdel Rahim al-Kib's office said in a statement.
"To reinforce this, the government has ordered the army chief and the interior ministry to consider the area of clashes a military zone and to use force and all means necessary to stop any shooting against innocent civilians."
The statement was backed by the ruling National Transitional Council and Dar al-Fitna, which represents Libya's highest religious authority.
The interim government called for the opening of safe passages to allow for the evacuation of the wounded and the delivery of humanitarian aid, and it commissioned a fact-finding mission to investigate the roots of the conflict.
The fighting which erupted Monday has pitted fighters of the Mashashia tribe against gunmen from the Gontrar tribe and the town of Zintan, 170 kilometers (105 miles) from Tripoli, according to official state media and local sources.
Sources in Gheryan, a city near the fighting zones, told AFP that dozens of families streamed in on Saturday seeking shelter from the fighting, while army spokesman Ali al-Sheikhi told AFP the "clashes were ongoing."
Several health ministry officials said the number of casualties was rising although they could not give numbers.
On Wednesday, the interim government said the fighting had claimed 14 lives and left more than 89 wounded.
Several sources say the clashes erupted after a resident of Zintan was killed at a roadblock set up by Mashashia tribesmen.
The tribesmen, meanwhile, accuse Zintan forces of shelling their village, Sheguiga, with tank and rocket fire.
Tensions have been high between former rebels in Zintan and Mashashia tribesmen since the 2011 uprising that toppled Libyan dictator Moamer Kadhafi.
Zintan fighters are credited with having led the units which captured Tripoli from Kadhafi's forces last August. They also detained the slain dictator's son, Seif al-Islam, on November 19 and have held him since.
The Mashashia are accused of having backed Kadhafi's regime in last year's conflict.
Clashes between former rebels from Zintan and Mashashia tribesmen killed four people in December.