Six civilians, including a child, have reportedly been killed following renewed clashes near the port city of Derna, according to the UN Office for the Coordination of Humanitarian Affairs.
Fourteen injuries and at least 47 casualties among armed forces have also been reported, as well as damage to civilian homes. Some 300 to 500 families have fled the city.
General Khalifa Haftar's Libyan National Army (LNA) advanced this week on villages four kilometres from Derna, the last major bastion of opposition to the LNA in the east of the country.
Troops were targeting a coalition of extremists and rebel veterans known as the Derna Mujahideen Shura Council (DMSC) and were advancing on five frontlines supported by air strikes and artillery, said Abdel-Karim Sabra, a spokesman for the operation.
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According to UAE state agency WAM, LNA forces captured a wheat silo and a number of villages on the outskirts of the city.
"Zero hour for the liberation of Derna has struck. Our army forces are now targeting their hideouts," General Haftar announced earlier in May.
“We have given instructions to avoid civilians,” he said. “The peace efforts in Derna have reached a dead end.”
On 14 April, the LNA started to make advances towards Ain Mara in western Derna. Since then, airstrikes, shelling, artillery fire and fighting between armed forces has been ongoing.
The LNA has surrounded the city on the coastal highway between Benghazi and Egypt, and has long threatened to begin ground operations there. Its campaign had previously been limited to occasional air strikes and bombardments.
Clashes have occurred in outlying villages around the besieged city and according to the UN, further displacements are expected as fighting moves closer to the urban centre.
In November 2014 Derna was captured by ISIS. The DMSC, composed of locally-raised militias, pushed ISIS out of town the next June. Egypt has in the past launched air strikes against what it said were terrorist training camps operating in the town.
But even before the toppling of Muammar Qaddafi, Derna was known as a bastion for militants.
General Haftar's health scare in April and consequent absence had fuelled rumours about his health on Libyan social media. Some outlets even went as far as announcing his death, paving the way for speculation about his successor.
Tim Eaton, an analyst with London-based Chatham House, said the timing of the Derna offensive "may be in part motivated by Haftar's desire to restate his strongman credentials."