Libya has 'best opportunity' for peace in decade: US official

War-torn Libya has its best chance for peace since the fall of dictator Moamer Kadhafi, a senior US diplomat said Wednesday, urging rival sides to work together ahead of December elections.

"Libya now faces the best opportunity it has had in a decade, to bring the conflict to closure, to move the economy forward and to lay the foundation for a stable democratic society," said Department of State Counsellor Derek Chollet during a visit to Tripoli.

"The US will continue to support this vital process," he told journalists.

But speaking after meeting top figures in the country's transitional government including Prime Minister Abdulhamid Dbeibah, he warned that "the moment is urgent".

Chollet's visit came days after parliament speaker Aguila Saleh, a key backer of eastern military strongman Khalifa Haftar, ratified a law governing the upcoming presidential election, sparking anger from MPs and politicians who say he failed to follow due process.

Libya tumbled into chaos following the US and NATO-backed 2011 revolt that toppled and killed Kadhafi, with rival militias and foreign powers fighting for control.

A war between west Libya forces and Haftar came to a formal halt with a UN-backed ceasefire in October last year, and the world body has since been overseeing a complex peace process with elections set for December 24.

But the legal basis for the elections has been the focus of growing tensions between various sides.

Last week, a spokesman for the eastern-based parliament elected in 2014 published the text of the presidential elections law, signed by Saleh.

But some lawmakers were quick to criticise Saleh for not submitting the full text to a parliamentary vote, and the High Council of State (equivalent to a Senate), accused him of trying to "grab powers" and hamper the upcoming elections.

Saleh has long been accused of trying to favour Haftar, a likely candidate for the presidency who controls the country's eastern province and part of the south.

On Wednesday, Chollet said "the recent... proposal is a solid basis for discussion" and urged top officials to "proceed, without delay, on ways to move this forward".

"We ask only one thing of Libyan leaders: that they contribute constructively on what is on offer rather than tear it down while offering nothing instead."

The United States led the 2011 invasion of Libya but has had a fairly hands-off approach since 2012, when an assault on the US consulate in Benghazi killed four Americans, including ambassador Chris Stevens.