Three days of clashes between tribes in the southern Libyan town of Sabha have killed more than 70 people, a Libyan government spokesman has said.

"It is regrettable that more than 70 people have been killed and more than 150 have been wounded" since Monday in the desert town of Sabha, Nasser al-Manaa told a news conference in Tripoli on Wednesday.

Local officials said the fighting pitting the African Toubou tribe against Arab tribes in Sabha had eased and efforts to secure a truce were underway, although the Toubou claimed they were facing a "massacre."

"There are still clashes but not as intense," in Sabha, said Abdelmajid Seif al-Nasser, a town official who quit his post on Tuesday from the ruling National Transitional Council in protest over the violence.

"The national army and a committee of elders have entered the town in a bid to secure a truce," Nasser, who represented the NTC in Sabha, told AFP news agency.

But Toubou tribesmen said Arab tribesmen from Sabha were "surrounding" them in the Tayuri and Al-Hijara neighbourhoods and shelling them since the early hours of the morning.

"Al-Hijara is surrounded from all sides. All the Arab (tribes) are against us. They are bombarding us using all sorts of rockets indiscriminately. It is a real massacre," said Karima Jaber, a Sabha airport employee.

‘Ethnic cleansing’

Toubou chief Issa Abdel Majid Mansur said earlier this week that 40 members of his tribe had been killed, and accused Libyan authorities of using warplanes and tanks against his community.

Speaking to AFP, Mansur denounced what he said was a plan to "ethnically cleanse" his people, and raised the threat of a separatist bid.

"We announce the reactivation of the Toubou Front for the Salvation of Libya [TFSL, an opposition group active under the former regime] to protect the Toubou people from ethnic cleansing," Mansur said.

"If necessary, we will demand international intervention and work towards the creation of a state, as in South Sudan," he said.

Ali al-Dib, a former rebel, said the clashes erupted in the city centre when the Toubou refused to hand over to local authorities one of their men accused of killing a member of the Bussif tribe.

The Toubou are black oasis farmers by tradition who also have connections beyond Libya's borders.

They live in southern Libya, northern Chad and in Niger, and have previously denied having separatist ambitions.