UN envoy Bernardino Leon insisted Wednesday that troubled Libyan peace talks were not yet over but acknowledged they were at a crossroads that might force him to step down as mediator.

Leon said the coming days would decide whether there was any future in his mission to broker a deal between the North African nation's rival parliaments in the capital Tripoli and the eastern town of Tobruk.

The Spanish diplomat has been trying for months to come up with a compromise between the conflicting claims of the two assemblies that will allow the formation of a unity government to tackle the rise of jihadist groups and people smuggling across the Mediterranean to Europe.

But successive proposals have met with objections from one side or the other, the latest from the Tobruk parliament which is recognised by most of the international community.

It issued a statement late on Tuesday rejecting Leon's latest proposals designed to win over Tripoli and demanding that he go back to the previous draft.

The UN envoy played down that statement.

"I don't think that Tobruk has rejected our proposal -- according to what I'm hearing, there was no quorum, it was simply a statement backed by some lawmakers but not enough to constitute a consensus of the parliament," he said.

Leon said he still hoped the rival sides would return to the talks venue in the Moroccan seaside resort of Skhirat later on Wednesday or on Thursday but admitted he still had no decision to do so from either.

He acknowledged that time was running out for his mediation mission but said he had not given up hope.

"Of course, if there's a decision be it on September 20, before then, or in the days that follow not to continue the process, then of course my time as representative and special envoy will be over but we're not there yet."

He appealed to both sides to compromise so that they could tackle the rise of the Islamic State jihadist group and Libya's emergence as a smuggling hub for migrants risking their lives to cross the Mediterranean.

"If we sign, Daesh (IS) will still be there, mafias trafficking in people will still be there, but we will have a chance," he said.