BENGHAZI, Libya (Reuters) - At least 60 people were killed as rival Libyan forces clashed at a southern air base on Thursday, medical and military officials said, dimming hopes that tensions in the area can be calmed.

The violence erupted after a brigade from the western city of Misrata attacked Brak Al-Shati base, which they had previously ceded to an opposing faction aligned with the eastern-based Libyan National Army (LNA).

The two sides are attached to loose and shifting alliances based in the east and west of Libya that have vied for power over the past three years, deepening the divisions that surfaced with the country’s 2011 uprising.

A medical source in Brak Al-Shati said 60 bodies had been brought to a hospital there, including members of the LNA-aligned 12th Brigade and civilians who appeared to have been summarily killed.

The mayor of Brak Al-Shati, Ibrahim Zemmi, told local media that the number of dead from the 12th Brigade alone was 74, with a further 18 wounded. A 12th Brigade spokesman, Mohamed Al-Afirs, said as many as 86 people had been killed including his brigade’s troops and civilians.

The death toll could not be independently verified. If confirmed it could mark a major escalation in Libya’s stop-start conflict in which fighting breaks out frequently but casualty figures are often low.

Over the past few months the area around Brak Al-Shati, including another base at Tamanhent and the southern city of Sabha, has become a flashpoint between forces loyal to the LNA, led by eastern-based commander Khalifa Haftar, and rivals who are aligned with current and former governments in Tripoli and draw on support from Misrata.

A spokesman for the Misrata-based Third Force, Mohamed Gliwan, said they had attacked the base because they had detected “suspicious movements” inside, and that the base had become a threat under 12th Brigade commander Mohamed Bin Nayel.

“We left the base before as part of our military strategy, and we attacked it because Bin Nayel and his people were targeting Tamanhent,” Gliwan told Libya Al-Ahrar TV. “We liberated the base and destroyed all the forces inside.” He did not give casualty figures.

LNA spokesman Ahmed al-Mismari said the base was targeted because the attackers thought the 12th Brigade were away after attending a major military parade near Benghazi. He said the 12th Brigade arrived back at the base shortly after the attack began.

Mismari said the 12th Brigade had eventually repelled the attack. Gliwan said the Third Force had stationed themselves outside the base because they were concerned about retaliatory air strikes, but were positioned to target the 12th Brigade with shelling.

Earlier this month Haftar broke a long deadlock by meeting the head of the United Nations-backed government in Tripoli, and both agreed to try to calm the situation in the south.