MOSCOW — Syria’s warring sides and the mediators meeting in Kazakhstan failed to agree on the formation of a committee meant to draft a new constitution for the war-torn country, the U.N. special envoy to Syria said Thursday, calling it a “missed opportunity.”

Staffan de Mistura was in the Kazakh capital of Astana where Russia, Turkey and Iran are holding talks with the Syrian government and the opposition to try and end the seven-year civil war that has killed some 400,000 people. The committee had been expected to be formed before the end of the year.

Meanwhile, U.S forces set up new observation points in a Syrian town controlled by its Kurdish-led Syrian allies along the border with Turkey in northeastern Syria. The area has been the scene of recent tension after Turkey forces shelled Kurdish positions there.

U.S.-led coalition spokesman Sean Ryan said Thursday the forces are securing locations for manned observation posts along the border "to support security and stability" in the area. Ryan said the posts are not permanent structures and aim to keep "all parties focusing" on fighting Islamic State group militants, who still have a stronghold to the south.

Turkey considers the Syrian Kurdish militia an extension of the Kurdish insurgency within Turkey. The U.S-led coalition supports the Kurdish-led forces who retook large areas in eastern Syria from ISIS.

Last week, Turkish Defense Minister Hulusi Akar said he had voiced Turkish concerns over U.S. plans to set up the posts during meetings with U.S. officials.

“I believe that such a practice will make the already complex situation even more complex,” Akar said, calling on the U.S. to “immediately” cut off ties with the Syrian Kurdish militia.

U.S. and Turkish soldiers conduct the first-ever combined joint patrol on Nov. 1, 2018, outside Manbij, Syria. (Spc. Arnada Jones/Army)
U.S. and Turkish soldiers conduct the first-ever combined joint patrol on Nov. 1, 2018, outside Manbij, Syria. (Spc. Arnada Jones/Army)

Control over the constitutional process has been a key point of conflict between President Bashar Assad’s government and the international community and Syrian opposition.

Assad has said his government will only consider amendments to the current constitution, in defiance of a U.N. initiative to have the government, opposition and independents draft a new document.

"Envoy de Mistura deeply regrets that at a special meeting in Astana with the three Sochi co-conveners, there was no tangible progress in overcoming the ten-month stalemate on the composition of the constitutional committee," said a statement released by his office.

It added that this was the last meeting in Astana this year and it "has, sadly for the Syrian people, been a missed opportunity to accelerate the establishment of a credible, balanced and inclusive, Syrian-owned, Syrian-led, UN-facilitated constitutional committee."

Russian envoy for Syria Alexander Lavrentyev told Russian news agencies after the meeting that the work to form the committee may stretch into next year.

De Mistura's statement came hours after Syria's U.N. ambassador urged Western powers to lift crippling economic sanctions against the war-torn country if they are serious about helping millions of Syrian refugees to return to their homeland.

Bashar Ja'afari spoke in Astana where the mediators are speaking separately to the warring sides, which are not meeting face to face.

Nearly 6 million Syrians have fled the civil war, now in its eighth year, to neighboring countries and Europe. Syria and Russia, one of its main backers, insist that the refugees can safety return home now while many Syrians fear that they will face persecution.

Ja'afari said that lifting the sanctions imposed on Syria would be "the real test" for the West.

“If the West wants to really help us and the countries who are hosting refugees, they must start by lifting the economic sanctions,” he said. “So that these people who are abroad can return to their jobs, resume normal life and find work opportunity and are able to contribute to revitalizing the economy in Syria.”

Europe says it will keep its sanctions in place as long as "repression" continues in Syria, extending the measures to 2019.

Ahmed Tumah, Syrian opposition representative in Astana, said the return of refugees should be arranged only after there is a political solution in place.

"Our problem with the regime is political," he said. "The regime doesn't want to take any step on the political level, only militarily."

In his comments to reporters, Ja'afari said that all foreign "illegitimate" forces should pull out of the country if the intention is to help end the Syrian crisis. He named the U.S., Turkish, French and British forces and estimated there were around 11,000 Turkish soldiers in northern Syria.

Associated Press writers Suzan Fraser in Ankara, Turkey and Sarah El Deeb in Beirut contributed to this report.