Syria’s Foreign Ministry dismisses the move as “unconstitutional and worthless” and a major opposition group warns against it too.
A bid to set up a federal region in Kurdish-controlled parts of northern Syria has been rejected by the government in Damascus and the opposition.
The move came as Russian President Vladimir Putin warned Moscow could build up its forces in Syria “in a few hours” if necessary.
Nawaf Khalil, an official with the Democratic Union Party, or PYD, said a Kurdish conference in Rmeilan in the northeastern province of Hassakeh had backed plans for a “democratic federal system”.
He said the new federal region would take in three enclaves currently under Kurdish control – Jazira, Kobani and Afrin – and would include Turkmen, Arabs and Christians, as well as Kurds.
But Syria’s Foreign Ministry rejected the move as “unconstitutional and worthless” and warned against any attempt to encroach upon Syrian territory.
The Syrian National Coalition, one of the country’s main opposition groups, also said it rejects unilateral declarations.
It warned against forming autonomous regions that “confiscate the will of the Syrian people”.
Meanwhile, Mr Putin said Moscow’s partial withdrawal of Russian warplanes from Syria earlier this week should not be misinterpreted.
He said Russia will maintain a strong military presence in the country after a five-and-a-half-month air campaign that has helped turn the tide of the five-year civil war.
Mr Putin said Syrian President Bashar al Assad had been informed in advance about the Russian pullout and supported it.
He also praised Mr Assad for what he described as his readiness to contribute to a peaceful settlement.
“We have seen him shown restraint and demonstrating a sincere striving for peace and readiness for compromise and dialogue,” he said.
Mr Putin also voiced hope that the partial withdrawal of Russian forces from Syria would help the UN-supervised peace talks that began in Geneva on Monday.