Libyan strongman Khalifa Haftar has said he will support 2018 elections in the war-torn country but also implied he would seize power if the polls did not occur.

Late Thursday, Haftar said presidential and parliamentary elections were "a fundamental solution" to Libya's crisis and should be held "without delay or fraud".

Oil-rich Libya has been wracked by chaos since a 2011 uprising that toppled longtime dictator Moamer Kadhafi.

A UN-backed unity government in Tripoli has failed to impose its authority nationwide, and has been rejected by a rival administration backed by Haftar in the east of the country.

This month, Haftar said the unity government had definitively lost all legitimacy after the expiry of the December 2015 UN-brokered agreement that gave rise to it.

"But the accord is one thing and the UN mission's work (towards holding elections) is another," he told the Al-Hadath television channel Thursday.

Haftar's opponents accuse him of wanting to seize power and establish a military dictatorship, while his supporters have called for him to take control by "popular mandate".

Haftar said this "mandate" could be a possibility "if all classic mechanisms allowing a peaceful power transition via free and democratic elections were exhausted".

The UN Security Council has insisted the December 2015 deal remains the "only viable framework to end the Libyan political crisis" and prepare for elections.