ASTANA - The United Nations envoy on Syria signed off from his posting Thursday ruing "a missed opportunity" to help end the country's long conflict at talks in Kazakhstan's capital Astana.
Staffan de Mistura, who announced his resignation last month, capped his term as peace envoy with two days of talks in the Kazakh capital sponsored by power-brokers Russia and Iran -- allies of the Syrian regime of Bashar al-Assad -- and rebel-backer Turkey.
A statement from his office noted he regretted that "no tangible progress in overcoming the 10-month stalemate on the composition of the constitutional committee" was made at the talks.
The meeting in Astana was "a missed opportunity to accelerate the establishment of a credible, balanced and inclusive, Syrian-owned, Syrian-led, UN-facilitated constitutional committee," the statement said.
The two-day negotiations that concluded Thursday, are the 11th in Astana since Moscow began a diplomatic push in early 2017 that effectively sidelined other talks on Syria led by the United Nations.
The constitutional committee is viewed as a vital element in reaching a political settlement in the country.
Speaking after the talks, Russia's Syria negotiator Aleksandr Lavrentyev said the committee was of "upmost importance".
"I want to say that we are sufficiently close to our cherished goal," he added, without giving any date.
The talks began Wednesday with a 10-week-old Idlib truce deal hanging in the balance after an alleged chemical attack in the government-held city of Aleppo on Saturday triggered retaliatory raids.
The exact circumstances of the attack remain murky and bitterly disputed.
The Syrian government of Bashar al-Assad has blamed rebel fighters for the attack which the Syrian Observatory for Human Rights said hospitalised 94 people.
The incident has strained an already fragile agreement reached in mid-September to fend off a fully-fledged assault on Idlib, which Syria's regime -- backed by Russia and Iran -- has said it is committed to re-taking.
Speaking late Wednesday, Russia's Lavrentyev said that "additional time" would be required to secure a buffer zone in the region of three million people after an uptick in fighting.
The alleged chemical attack "must be dealt with very seriously," he said, calling for qualified international bodies to visit the city to assess the incident.
On Sunday, Russia said its war planes had carried out their first strikes in the zone since the deal was reached, in an apparent retaliation.
No space for Washington
The Astana talks have seen the United States and other Western countries kept at arm's length over Syria.
A joint communique agreed by the three sponsors targeted Washington's continued military presence in the country.
The guarantors "rejected all attempts to create new realities on the ground under the pretext of combating terrorism," it said.
Earlier this week Turkish President Recep Tayyip Erdogan accused the US of using the presence of the Islamic State group in southern Syria as an excuse to keep forces stationed there.
Lavrentyev also complained of the extended US presence during the talks in Astana.
The United States has attended some previous Astana rounds as an observer but US Special Representative for Syria Engagement James Jeffrey last week ruled out Washington participating in the latest talks.
The next set of Syria negotiations in Astana are scheduled for early February, according to the joint communique.
Syria's grinding seven-year civil war has killed more than 360,000 people and displaced millions.