PARIS (Reuters) - The Syrian Kurdish YPG militia and its political arm the PYD will not be invited to planned peace talks in Kazakhstan, a PYD official said on Tuesday, an outcome that would leave a key player in the conflict off the negotiating table.

A Kurdish fighter from the People's Protection Units (YPG) carries his weapon as he walks at the faculty of economics where a defaced picture of Syrian President Bashar al-Assad is seen in the background, in the Ghwairan neighborhood of Hasaka, Syria, August 22, 2016. REUTERS/Rodi Said

Syria’s government and rebel forces started a ceasefire on Dec. 31 as a first step toward face-to face negotiations backed by Turkey and Russia, but the date and its participants remain unclear.

The truce is also under growing strain as rebels have vowed to respond to government violations and President Bashar al-Assad said on Monday the army would retake an important rebel-held area near Damascus.

“We are not invited. That’s for sure,” Khaled Eissa, a PYD member told Reuters in France. “It seems there were some vetoes. Neither the PYD or our military formation will be present,” he said.

Assad’s ally Russia had previously sought the PYD’s presence at other negotiations in Switzerland.

But Turkey, which opposes Assad, regards both the YPG and PYD as extensions of the Kurdistan Workers Party (PKK) separatists in its own territory and has said two groups should not be represented in Astana.

The Syrian Kurds aim to cement the autonomy of areas of northern Syria where Kurdish groups have already carved out self-governing regions since the start of the war in 2011, though Kurdish leaders say an independent state is not the goal.

“What we have been told is that there will only be a limited number of armed groups and not political groups,” Eissa said, adding that for a comprehensive peace deal in Syria the Kurds would at one point have to be invited to the negotiating table.

The main Syrian political opposition umbrella group that includes about half a dozen armed groups, the Riyadh-backed High Negotiations Committee, is meeting in the Saudi capital later this week to discuss the Astana talks, although it is also unclear whether Moscow intends to invite them, diplomats and opposition officials said.

Ankara intervened in Syria last year in support of rebel groups fighting under the Free Syrian Army (FSA) banner sought to drive Islamic State from positions it had used to shell Turkish towns, and also to stop YPG expansion.

The YPG and its allies backed by a U.S.-led coalition is fighting against IS militants around the group’s Syrian bastion Raqqa, while Turkish-backed rebels are fighting the jihadist group further northwest near areas under Kurdish control.