The outlawed PKK and its Syrian offshoot the Democratic Union Party (PYD) and their allies were preparing to approve a draft for a system of federal government in northern Syria this week, officials said, reaffirming their plans for autonomy while Russia and Turkey seek to establish a nation-wide ceasefire in Syria.

The aim is to cement the autonomy of areas in northern Syria where terrorist YPG, which is the armed branch of PYD, and their allies have already carved out self-governing regions since the start of the war in 2011.

Increasing YPG influence in northern Syria has alarmed neighboring Turkey, while the U.S. also opposed the federal plan first announced in March. The Assad regime also opposes federalism.

The blueprint amounts to a constitution, known as the social contract, and was expected to be approved on Wednesday or Thursday at a meeting of a 151-member council in the city of Rmeilan, according to Hadiya Yousef, who chairs the council.

"I expect ratification because we have discussed the content with all groups and political sides repeatedly, and the draft was worded with consensus," she said in a written message.

"We will clarify through the contract... the means for starting the formation of our institutions and administrative system, and we will start preparations for elections," she added. The first elections would be on regional administrations, to be followed by an election of a central body.

The council, a constituent assembly which officials say includes members of all the main political, ethnic and religious groups in the area, began meeting on Tuesday.

Unilateral moves by YPG and their allies have taken place against a backdrop of international failure to promote a political settlement to a Syrian war nearing its sixth anniversary.

Russia, Iran and Turkey said last week they were ready to help broker a peace deal in Syria after meeting in Moscow, where they adopted a declaration setting out the principles any agreement should adhere to.

Arrangements for the talks, which would not include the U.S. and be distinct from separate, intermittent U.N.-brokered negotiations, remain hazy, but Moscow has said they would take place in Kazakhstan, a close ally.

Iran and Russia have given Assad crucial military backing in the war against opposition groups fighting him in western Syria. Turkey has been a major backer of the moderate opposition.

The effort to revive the diplomatic track follows the defeat of Syrian opposition in eastern Aleppo, Assad's biggest victory of the war. The main militia, the PKK-affiliated YPG, has mostly avoided conflict with Assad, while serving as the military backbone for a possible autonomous region.

The YPG is the dominant force in the Syrian Democratic Forces (SDF) alliance that has seized swathes of territory from Daesh in a U.S.-backed campaign in Syria, and Turkey considers it as a terrorist organization for its links with the PKK terrorist group.

Another PYD-affiliated politician said groups signing up to the new constitution were not ruling out involvement in future peace talks, but they had not been invited to a meeting in Kazakhstan.

"We are ready to negotiate in any regional or international meeting, to propose our plans and our vision for a solution in Syria," said Fawza Ahmad, a member of the constituent council. She noted that PYD-linked groups were also excluded from previous U.N.-backed talks on Syria.

Turkey launched a military operation into northern Syria in August against terrorist organizations threatening its security.