Syrian Civil Defence volunteers rescue children from a damaged building following a reported airstrike that targeted the Idlib bus station on January 18, 2017
Beirut (AFP) - Key rebel group Ahrar al-Sham said on Wednesday it will not take part in peace talks in the Kazakh capital next week aimed at ending Syria's nearly six-year-old war.
The announcement came as Russia and Turkey -- which along with Iran organised the talks starting in Astana on Monday -- carried out their first joint air strikes against the Islamic State jihadist group in the war-torn country.
Ahrar al-Sham, which counts thousands of fighters in central and northern Syria, said it would not attend the Astana talks due to "the lack of implementation of the ceasefire" in force since December 30 and ongoing Russian air strikes over Syria.
The Islamist faction was among the signatories of the ceasefire deal that does not include IS and Fateh al-Sham, which changed its name from Al-Nusra Front after breaking ties with Al-Qaeda.
The truce, brokered by regime supporter Russia and rebel backer Turkey, has largely held across Syria although fighting has persisted in some areas.
Ahrar al-Sham cited "the regime's offensive against our people in Wadi Barada", an area 15 kilometres (10 miles) northwest of Damascus that is the capital's main source of water, among its reasons for staying away from the talks.
President Bashar al-Assad's forces have pressed an assault to retake the area from rebels after mains supplies were cut last month, leaving 5.5 million people in Damascus and its suburbs without water.
Ahrar al-Sham said however that it would support decisions taken by other rebel groups represented at the Astana talks if they were "in the interest of the nation".
Mohammad Alloush of the Jaish al-Islam (Army of Islam) faction will lead a "military delegation" in Astana of around eight people, backed by nine legal and political advisors from the High Negotiations Committee umbrella group.
Syria's UN ambassador Bashar al-Jaafari is to head the government delegation.
- US involvement? -
Regime and rebel figures are headed for Kazakhstan with diametrically opposed approaches to the aims of the talks.
Damascus has insisted it will seek a "comprehensive" political solution to the conflict, while rebels say they will focus solely on reinforcing the frail nationwide truce.
Next week's talks mark the first time since the conflict began in 2011 that the United States has not been at the centre of peace negotiations.
Iranian officials said on Wednesday they were strongly opposed to Washington joining the talks.
Turkey and Russia -- which started air strikes in support of Assad's regime in 2015 -- have however said the new US administration of Donald Trump should be represented.
Around the town of Al-Bab in Syria's northern province of Aleppo, nine Russian and eight Turkish planes on Wednesday took part in the "first joint air operation" against IS, a Russian military official said, destroying "36 targets".
IS has faced assaults on several fronts since it overran large parts of Syria and neighbouring Iraq in 2014.
- IS smokescreen -
In the eastern city of Deir Ezzor, the jihadist group set tyres ablaze to create a smokescreen from regime and Russian warplanes on Wednesday as fierce clashes gripped the city, the Syrian Observatory for Human Rights said.
IS launched a fierce assault on Saturday to capture the government-held third of Deir Ezzor city, as well as the adjacent military airport.
Since Saturday, 160 people have been killed -- 75 IS militants, 46 regime fighters and 39 civilians -- according to the Britain-based Observatory.
An activist group said IS had executed 10 regime fighters captured during the jihadist onslaught.
Besieged by IS since early 2015, the regime-controlled part of Deir Ezzor city is home to around 100,000 people.
Residents on Wednesday said they were terrified of falling victim to the mass killings for which the jihadists have become infamous.
"Civilians in the city are terrified and anxious, afraid that IS will enter (government-held parts of) the city since they accuse us of being 'regime thugs'," said Abu Nour, 51.
He said fellow residents were haunted by previous abductions and mass executions carried out by IS in the broader oil-rich province of the same name, most of which is controlled by IS.
The UN's World Food Programme said on Tuesday it could no longer carry out air drops above Deir Ezzor because of the fighting.
Syria's war has killed more than 310,000 people and displaced thousands since it erupted in March 2011 with a brutal repression of anti-government protests.