Authorities in Libya's militia-held capital have called for a freeze in UN-mediated peace talks until the military of the internationally recognised government halts an offensive in the east.

Khalifa Ghweil, prime minister in a Tripoli-based parallel administration, "strongly" condemned the talks being held in Morocco between Libya's rival parliaments.

The UN-drafted accord under discussion was "suspect and contains articles which run contrary to the nation's immovable principles and the objectives" of the 2011 revolution which overthrew longtime dictator Moamer Kadhafi, he said in a televised speech on Tuesday night.

Libya has had two parliaments and two governments since August 2014 when Islamist-backed militias seized Tripoli, prompting the government recognised by most of the international community to take refuge in the far east.

While acknowledging some delegates from the legislature in the capital were taking part in the talks in apparent defiance of his administration, Ghweil urged the Libyan people "to freeze this dialogue until the offensive is halted", in reference to the rival government's military offensive.

He called for "an inter-Libyan dialogue on Libyan soil to resolve the Libyan crisis, leading to a settlement that satisfies all parties while respecting the aims" of the revolution.

UN envoy Bernardino Leon told Libya's warring parties on Tuesday there would be no more negotiations on the peace plan drawn up in the seaside resort of Skhirat near Morocco's capital.

He told delegates he expected a straight yes or no answer when they return from a recess for the Muslim holidays of Eid al-Adha that run from Wednesday until Sunday.

Leon has been trying for months to come up with a compromise between the conflicting claims of the two administrations that will allow the formation of a united 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, and the Spanish diplomat ruled out any more redrafting.

On Sunday, the UN Support Mission in Libya condemned the offensive in the second city of Benghazi announced last week by army chief Khalifa Haftar, saying it was an attempt to sabotage peace talks.