GENEVA/ASTANA (Reuters) - Russia, Turkey and Iran failed to make any concrete progress in setting up a Syrian constitutional committee at a meeting in the Kazakh capital Astana on Thursday, the office of U.N. Syria envoy Staffan de Mistura said.

UN Special Envoy for Syria Staffan de Mistura attends a meeting during consultations on Syria at the European headquarters of the United Nations in Geneva, Switzerland September 11, 2018. Salvatore Di Nolfi/Pool via REUTERS

As part of U.N.-mandated political reforms to end Syria’s war, the country’s constitution is supposed to be reformed and new elections held. But Syria’s government has rejected U.N. involvement in picking the members of the committee to make the changes, and the process has gone nowhere since January.

“Special Envoy de Mistura deeply regrets ... there was no tangible progress in overcoming the ten-month stalemate on the composition of the constitutional committee,” his office said.

“This ... 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,” it added.

The three countries said in a joint statement issued after the talks that they would “intensify” consultations to establish the committee as soon as possible. Russia’s Syria envoy Alexander Lavrentiev said the outcome was “positive”.

Amid the political stalemate, Damascus’ ally Russia, and Turkey, which backs Syrian rebels, agreed in September to create a de-militarization buffer zone around Syria’s insurgent-held northwestern Idlib enclave.

But shelling exchanges have been common since then and the first air strikes since the deal hit the area on Sunday.

On Thursday, Ankara, Moscow and Tehran, which also backs the Syrian government, said they were concerned with ceasefire violations and “would step up their efforts to ensure observance”, but stressed the need to continue to “fight against terrorism” there.

De Mistura’s humanitarian adviser Jan Egeland told Reuters in an interview in Geneva that Russia and Turkey needed to negotiate with the armed groups in Idlib, even those listed as terrorists, to protect civilians and to foster the reconciliation needed to bring peace.

“Many are very nasty types but it would be tremendous a mistake to give them no option but to fight to the last man and the last civilian in the areas they control,” he said.

The U.S. State Department said it was vital to convene the constitutional committee and accused Russia and Iran of continuing “to use the process to mask the Assad regime’s refusal to engage in the political process,” referring to Syrian President Bashar al-Assad.