ASTANA (Reuters) - Russia and regional powers Turkey and Iran backed a shaky truce between Syria's warring parties on Tuesday and agreed to monitor its compliance, but on the ground rebels faced continued fighting on two fronts which could undermine the deal.
After two days of deliberations in Astana, Kazakhstan's Foreign Minister Kairat Abdrakhmanov said the powers had agreed in a final communique to establish a system "to observe and ensure full compliance with the ceasefire, prevent any provocations and determine all modalities of the ceasefire."
While welcoming the text, the Syrian government's chief negotiator Bashar Ja'afari said an offensive against rebels west of Damascus would carry on. Rebels say it is a major violation of the ceasefire agreed on Dec. 30.
Opposition negotiator Mohammad Alloush said he had reservations about the text which he said legitimized Iran's "bloodletting" in Syria and did not address the role of Shi'ite militias fighting rebels.
In northwest Syria, heavy fighting erupted between the jihadist group Jabhat Fateh al-Sham and Free Syrian Army factions who were represented at the Astana talks.
FSA groups are reeling after being driven from Aleppo city last month by government forces and their allies. Any further loss of territory in their main northern stronghold - this time at the hands of jihadist insurgents - could leave them too weak to achieve any meaningful gains from peace negotiations.
In Astana, rebel and government delegates held indirect talks for the first time in nine months at a time when Turkey, which backs the rebels, and Russia, which supports Syrian President Bashar al-Assad, want to disentangle themselves from the fighting.
That has led them into an ad-hoc alliance that also appears to enshrine Iran in a process that could lead to some form of political settlement - leaving the United Nations' role unclear, especially with the United States distracted by domestic issues.
The talks represent a coup for Moscow, which has evolved into the main powerbroker since its military intervention in September 2015 to shore up Assad. "We have managed ... to give birth to the Astana process," the head of the Russian delegation, Alexander Lavrentyev, told reporters.
The final text did not go into any details beyond reaffirming the Turkish-Russian Dec. 30 ceasefire. A Western diplomat said the three powers agreed to meet again in Astana on Feb. 6 to discuss the mechanism.
In Washington, the State Department called on Russia, Turkey and Iran "to press regime, pro-regime, and opposition forces to abide by the ceasefire in order to create an environment more conducive to intra-Syrian political discussions."
Acting spokesman Mark Toner said: "We look forward to the resumption of U.N.-sponsored intra-Syrian talks between the regime and opposition groups."
Since the ceasefire announcement, government-backed forces have launched an offensive northwest of Damascus in the Wadi Barada area, where fighting intensified on Tuesday.
The government and its allies, including Lebanese group Hezbollah were trying to push forward in Ain al-Fija, where springs and a pumping station that supply most of the capital's water are located.
Rebels had come to the meeting hoping Moscow would put pressure on the Iranians to curb military offensives.
"The Russians have moved from a stage of being a party in the fighting and are now exerting efforts to become a guarantor. They are finding a lot of obstacles from (Lebanon's Shi'ite) Hezbollah forces, Iran and the regime," Alloush told reporters after the talks.
He said he expected Russia to respond within a week to a rebel ceasefire proposal and that rebels would never allow Iran, which they accuse of trying to change the demographic make-up of certain Sunni Muslim areas, to have a say in Syria's future.
Government envoy Ja'afari said it was "pitiful" that some "armed terrorist groups in Astana" were criticizing Iran, one of the three guarantors.
Western diplomats attending the talks informally said despite a lack of detail about the ceasefire, it was positive that the final communique mentioned reviving the U.N. political talks in Geneva under U.N. resolution 2254 and that the three powers agreed to jointly fight Islamic State and Jabhat Fateh al-Sham, which changed its name from Nusra Front last year, and to separate them from armed opposition groups.
However, Assad's foreign backers and opponents have rarely agreed on exactly which fighters represent moderate rebel forces and which ones are jihadists.
The U.N. Special Envoy for Syria, Staffan de Mistura, who was attending the Astana talks, said he now hoped to reconvene peace talks in Geneva next month.
"We (the UN) are the main player in regards to the political process," de Mistura said. "The political process should continue in Geneva ... We cannot allow another ceasefire to be, in a way, wasted, because of a lack of a political process."
Additional reporting by Kinda Makieh, Denis Dyomkin and Lesley Wroughton; writing by John Irish; Editing by Janet Lawrence and Giles Elgood