The head of Libya's Presidency Council said on Saturday he would urge candidates in elections proposed for December not to take part unless there was consensus on the vote's legal framework.

Mohamed al-Menfi said it was his goal to make sure the national presidential and parliamentary elections went ahead as planned on December 24.

However, he said, "Not having a proper vision towards this election, (not having) this kind of consensus, is by itself a risk."

The elections were mandated as part of a roadmap drawn up last year by a political forum convened by the United Nations to end a decade-long crisis, but disputes over the vote threaten to unravel the peace process.

Libya has been wracked by conflict since the overthrow and killing of then head of state Muammar Gaddafi in 2011, and it was split after 2014 between warring western and eastern factions.

Besides setting elections, the UN-backed roadmap produced a new transitional administration to take over from the rival governments that had emerged in Tripoli and the east during the civil war.

The roadmap installed a three-man Presidency Council drawn from Libya's three regions and headed by Menfi to act as head of state, as well as a Government of National Unity (GNU) headed by Prime Minister Abdulhamid Dbeibah.

All sides in Libya and the foreign powers involved in the conflict say the elections must go ahead, but the UN-backed dialogue forum and Libya's existing institutions have not agreed on a constitutional basis for the vote.

"The problem is not about the legality of the laws; it's a political problem," said Menfi.

He said the legal basis for the election must be agreed on by both the House of Representatives (HoR), the eastern-based parliament, and the High State Council (HSC), an advisory body created in 2015 through a UN-backed political agreement aimed at ending the civil war.

"This is a constitutional path which is the main responsibility of the parliament and the High State Council," he said.

Potential candidates in the election include an array of factional leaders who divide opinion in Libya, and there are questions over whether any vote could be free or fair when armed groups control most of the country.

Menfi said it was vital to ensure that there was agreement on its legal basis before any election and that all candidates would agree to accept the results.

"If they don't reach consensus, then sacrifice – let's all withdraw from this process and step down," he said.

He said the Presidency Council would step in only if the other bodies – the HoR, the HSC, the UN and its dialogue forum – were unable to resolve a legal framework.

"Our goal is to make sure elections happen, and we hand over on the 24th whatever happens," he said.