Forces led by Khalifa Haftar launched an offensive on Tripoli in early April but the assault has stalled in the face of resistance from local armed groups aligned with the UN-recognised government in Tripoli.

Haftar and his backers say they are trying to free the capital from militias which they blame for destabilising Libya since the fall of Muammar Gaddafi in a NATO-backed uprising in 2011.

The campaign on Tripoli has left at least 653 dead and displaced more than 93,000, according to the UN, as well as causing extensive material damage.

Aguila Saleh, head of a parliament that relocated to eastern Libya in 2014 during a previous battle for Tripoli, said "the campaign to liberate Tripoli is not easy".

"More than two million Libyans are living in the capital and these armed groups are using people and buildings as shields," Saleh told Reuters in an interview during a visit to Cairo late on Wednesday.

He rejected any proposals for Haftar's Libyan National Army to withdraw or agree to a ceasefire.

"The (military) operation must be resolved. The political solution should in any case come even after the liberation of the Libyan capital," said Saleh.

"If someone could get these groups out peacefully, then the army would return to the barracks," he added, referring to the Tripoli armed groups.

Haftar's offensive has upended UN-led plans to stabilise Libya after years of conflict that have left the oil-rich nation divided and caused living standards to plummet.

Australian Associated Press