Syria’s main opposition negotiating body says it will boycott a peace conference in Russia next week.

The High Negotiations Committee announced the boycott of the Russia-backed conference in Sochi in a tweet after a vote held in Vienna, Austria, where a UN-led conference was being held.

Russia has been steering a separate negotiating track in Astana, and now in the Black Sea resort of Sochi where the conference is scheduled to be held on Monday with the participation of some 1,600 representatives of the Syrian government and opposition.

Opposition figures have said Russia, which backs Syrian President Bashar Assad’s forces, is trying to undermine the UN-led talks.

The boycott comes to the backdrop of escalating violence in northern Syria, where Turkey is attacking a Kurdish-held enclave.