Fighting near Tripoli has killed 121 people since strongman Khalifa Haftar launched an offensive earlier this month to take the Libyan capital, the World Health Organization said Sunday.

In clashes between Haftar's forces and those of the UN-backed Government of National Accord (GNA), both sides have proclaimed "advances" but neither appears to have made substantial progress on the ground in recent days.

With more than 560 people wounded since the fighting started on April 4, the WHO said it was sending more medical supplies and staff to Tripoli.

On its Twitter feed, the agency denounced "repeated attacks on health care workers" and vehicles during the fighting.

The UN's humanitarian coordination office, OCHA, said Saturday that three medical personnel had been killed and that shrapnel had put five ambulances out of action.

The mounting violence has sparked global alarm over the oil-rich country, in turmoil since NATO-backed forces overthrew former dictator Moamer Kadhafi in 2011.

The mounting violence has sparked global alarm about the oil-rich country Mahmud TURKIA, AFP

A bewildering array of militias have sought to take control since his ouster.

Haftar's offensive began shortly before a conference set for this month to discuss Libya's future -- an event the UN cancelled as his forces closed in on the capital.

Haftar, who leads the self-styled Libyan National Army (LNA), has pushed from his power base in the country's east towards the Libyan capital in the west, the seat of the UN-backed unity government led by Fayez al-Sarraj.

The unity government said its forces had shot down an LNA fighter jet on Sunday "that was preparing to conduct air raids" south of Tripoli.

An LNA source said the plane had come down in an area under its control and that the pilot, who had ejected, was "safe and sound".

That came as the strongman met in Cairo with key backer Egyptian President Abdel Fatah al-Sisi, who pledged support for "efforts to fight terrorism and extremist militias to achieve security and stability... throughout the country", Sisi's office said.

Haftar also has the support of key Gulf Arab states and Russia.

- 'Great advances' -

With gunfire echoing through city blocks and tanks rumbling through towns and districts south of Tripoli, many panicked residents have fled their homes.

More than 13,500 people have been displaced and over 900 are now living in shelters, OCHA said.

Both sides have launched daily air raids and accuse each other of targeting civilians.

Both sides have launched daily air raids and accuse each other of targeting civilians Mahmud TURKIA, AFP

One air strike the GNA blamed on Haftar's forces hit a school in Ain Zara, south of Tripoli, which has been the scene of violent clashes for days.

On Sunday, the UN mission in Libya warned that international humanitarian law "prohibits the bombing of schools, hospitals, ambulances and civilian areas".

The mission warned that it would document all breaches in order to inform the UN Security Council and the International Criminal Court.

The LNA meanwhile accused the Tripoli-based forces of an air raid "targeting civilians" in the Gasr Ben Ghachir region south of Tripoli.

GNA spokesman Mohamed Gnounou said his forces had carried out 21 air strikes targeting LNA positions and supply lines between Friday and Saturday.

- Terrorists and criminals? -

Gnounou late on Saturday claimed "great advances on all fronts", including in Al-Aziziya, a city about 50 kilometres south of Tripoli.

"We have not started this war," he said, "but we will decide the time and place of its end."

On the LNA's side meanwhile, spokesman Ahmad al-Mesmari said the attacking forces were also "moving forward on all fronts".

GNA spokesman Mohamad Gnounou said his forces had carries out 21 air strikes targeting LNA positions and supply lines between Friday and Saturday Mahmud TURKIA, AFP

He reiterated his claim that "terrorists" and "criminals" were fighting on the side of the UN-backed GNA forces.

"The decision is no longer in Sarraj's hands," he said. "It is in the hands of terrorists now."

The European Union also expressed its "concern" on Thursday at the involvement of "terrorist and criminal elements" in the fighting.

Sarraj on Saturday denounced the "misinformation campaign by some parties that our forces include fighters belonging to terrorist organisations and groups".

In a statement, he "strongly denied" the claim and insisted that it was the LNA attack on the capital that was "paving the way the way for dormant terrorist cells" to attack Libyans.