Ahrar al-Sham to stay away from Syria peace talks
The announcement came as Russia and Turkey - which along with Iran organised the talks starting in Astana on Monday - carried out their first joint airstrikes against the Islamic State 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 airstrikes over Syria.
The Islamist faction was among the signatories of the ceasefire deal that does not include IS and Fateh al-Sham Front, 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.
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 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.