Mediators in Tunisia's protracted political crisis urged the ruling Islamist party on Saturday to fully accept their roadmap for the way forward, saying its response so far had been "ambiguous".

The Ennahda party had issued a statement on Friday saying it accepted the blueprint for the formation of a government of independents and a national dialogue to finalise a new constitution and clear the way for elections.

But the mediators, who include the powerful UGTT trade union confederation as well as the employers' organisations Utica, said the party's response contained "ambiguities" and failed to clearly endorse all elements of the plan.

"We consider that the Ennahda statement is ambiguous and allows for manoeuvres, interpretations and multiple readings," said UGTT secretary general Houcine Abassi.

"We can't accept their agreement, as half of the roadmap is not given a precise response," he told a news conference.

An Ennahda statement on Saturday denounced this position, saying that the party had accepted the initiative and calling for "immediate talks on drawing up the constitution, a timetable for elections and forming a government".

The opposition has yet to give any public response to the blueprint, but Abassi said it had given its agreement.

The plan sets a three-week deadline for the formation of a cabinet of independents to replace the current Ennahda-led government after the launch of a national dialogue between the two sides.

It also sets a four-week deadline for the adoption of a new electoral law, the announcement of a timetable for fresh elections and the completion of a long-delayed draft constitution.

In its response, Ennahda gave a tighter deadline for the completion of the draft charter but did not spell out its position on the timetable for a new government.

Prompt replacement of the existing administration has been a persistent demand of the mainly secular opposition throughout the crisis triggered by the July 25 assassination of opposition MP Mohamed Brahmi, an attack that was blamed on hardline Islamists.

The opposition says Ennahda has failed to rein in jihadists, whose influence has grown since the 2011 uprising that toppled veteran president Zine El Abidine Beni Ali, and has not improved economic conditions.