TUNIS: The party of assassinated Tunisian politician Chokri Belaid will ask the U.N. Human Rights Council to investigate his killing because it lacks confidence in the judiciary’s handling of the case, its leaders said Monday.

The secular opposition leader’s assassination on Feb. 6 provoked the biggest street protests in Tunisia since the overthrow of strongman Zine al-Abidine Ben Ali.

“We agreed ... to go to the Human Rights Council in Geneva to request an investigation into the killing of Belaid because we have doubts in the Tunisian judiciary,” Zied Lakhdar, a leader in the Democratic Patriots Party, said. “We believe that the investigation was not serious and there is a lot of ambiguity and doubts.”

Mohammad Jmour, another leader in the party, said the Tunisian office of the U.N. High Commissioner for Human Rights had already been informed of the group’s concerns.

Tunisian authorities say they have arrested four hard-line Salafist Islamists in connection with the killing, but that the gunman who fired the fatal bullets is still on the run.

Tunisia’s moderate Islamist ruling party Ennahda has denied accusations by some of its opponents, including Belaid’s brother, that it was involved in the assassination.

Also Monday, Tunisia’s parliament was debating plans to set April 27 as the deadline for the finalization of the new constitution and Oct. 27 as the date for the next elections, as part of efforts to resolve a political crisis.

The deputy speaker of the National Constituent Assembly, Mehrezia Labidi, gave the dates in a posting on her Facebook page, as deputies met to draw up a calendar for the adoption of the constitution, as well as for elections.

Labidi, who belongs to Ennahda, did not give a precise timetable for the adoption of the constitution as each article must be approved by an absolute majority of MPs before the text is put to a vote. Unless it is approved by a two-thirds majority, it must be put to a referendum.

Several political timetables drawn up since Ennahda’s sweeping election victory in the first post-revolution poll have not been respected.

More than two years after mass protests that toppled Ben Ali and inspired revolutions in other Arab Spring countries, Tunisia is still without a fixed political system due to a lack of consensus between the main parties.

Ennahda is pushing for a pure parliamentary system while others are demanding that the president retain key powers.

Assembly Speaker Mustapha Ben Jaafar has called for an end to the tug-of-war, with the political uncertainty in Tunisia exacerbated by social tensions and the growing influence of militant Islamist groups.

“We must abandon narrow party interests even if that means making sacrifices, retreating. It is in the interests of Tunisians,” Ben Jaafar, whose secular Ettakatol is one of Ennahda’s partners in the outgoing three-party coalition, said at the weekend.

There are hopes that it may finally be able to overcome the crisis, which brought down the government of Hamadi Jabali, when parliament holds a vote of confidence Tuesday for premier-designate Ali Larayedh’s new Cabinet lineup.