* Government says sending force to intervene
* Third day of fighting between neighbours near western town
* Violence a test for the fragile government
* Ethnic and tribal conflicts rocking Libyan stability (Updates with death toll, interior minister)
By Taha Zargoun
TRIPOLI, April 3 (Reuters) - A flare-up of fighting between rival militias in the west of Libya has killed 14 people, the country's interim leadership said on Tuesday, and officials announced the despatch of a force to restore order.
The clashes, between members of the Berber ethnic minority and their Arab neighbours around the town of Zuwara, are a fresh test for the government which has struggled to assert its authority since a revolt last year ended Muammar Gaddafi's rule.
Militias from inside the predominantly Berber town, about 120 km (75 miles) west of the Libyan capital, were exchanging mortars and large-calibre fire with fighters from the nearby Arab settlements of Al-Jumail and Regdalin for a third day.
The fighting around Zuwara, on the Mediterranean coast, is typical of the kind of tribal and ethnic conflicts that have flared up since Gaddafi's fall.
In most cases the violence is the result of a toxic mix of vendettas that have been simmering for generations, the huge quantity of weapons in circulation since the revolt, and the lack of a strong central authority.
"There are heavy clashes at the entrance to Regdalin, (and) heavy bombing from Al-Jumail on Zuwara," Iyoub Sofian, from the Zuwara local council, told Reuters by telephone.
He said representatives from the national army had tried to broker a ceasefire on Monday, but it did not hold.
Mohammed al-Harizy, a spokesman for the National Transitional Council (NTC), told a news conference that four people from Zuwara were killed and 10 from the opposing side.
He also said 80 people had been injured on both sides and the fighting continued.
Fawzi Abdel A'al, the Interior Minister, earlier told reporters his men would intervene.
"We have prepared a force of 200 men from the Interior Ministry which has been directed to the region," he said in Tripoli. A'al said he was also coordinating with the national army for a contingent of troops to be sent to the area.
"I am asking the two sides to restrain themselves ... because there will be no winner in this battle," he said.
It was not clear though whether the national government could muster an effective force. It is still building its security forces. In the past it has had to request help from friendly militias to restore order because its own units were not up to the job.
From inside Zuwara, Sofian said two sides were exchanging mortar fire and anti-aircraft rounds from guns adapted to shoot at targets on the ground
"We stopped firing, but Al-Jumail and Regdalin did not stop the bombing, so we received orders to attack," Sofian said.
It was not immediately possible to contact fighters in Al-Jumail or Regdalin.
Zuwara lies on the main highway linking Tripoli to neighbouring Tunisia, a vital supply route for the Libyan capital.
An Interior Ministry official told Reuters the confrontation had started on Sunday when a group of Zuwara men hunting for game accidentally shot someone from Al-Jumail. They were briefly detained, angering people in Zuwara.
In another confrontation that has underlined Libya's fragility, about 150 people were killed in clashes over the past week between rival tribes in the southern city of Sabha. (Writing by Christian Lowe; Editing by Ben Harding)