Russia said Moscow, Washington and the United Nations will hold Syria talks in Geneva on Friday as diplomatic efforts to end the conflict are ratcheted up.
"We will be having consultations in the trilateral format -- Russia, the United States and the UN," Deputy Foreign Minister Gennady Gatilov told RIA Novosti state news agency on Wednesday.
UN peace envoy Staffan de Mistura is set to take part in the talks aimed at ending a brutal war that has killed more than 250,000 people and forced millions from their homes since March 2011.
Gatilov said Russia would be calling for the "intensification of joint efforts" in the "fight against terrorism".
Foreign Minister Sergei Lavrov, in a call with his US counterpart John Kerry Wednesday, said they needed to draw up a list of "terrorist groups that we must not talk to and that we must fight together", his ministry said.
Kerry said he would visit Moscow next week as Russia and the United States work to forge a framework for a Syrian ceasefire and political transition.
Moscow has sought, so far without success, to persuade nations in the US-led coalition that opposes Assad to work with its own forces flying a bombing campaign in Syria and with Damascus in a broader coalition against the Islamic State (IS) group.
Representatives from Syria's fragmented opposition on Wednesday began a two-day closed-door meeting in Saudi Arabia to seek a united front for potential talks with Syrian President Bashar al-Assad.
It was the first time a broad range of Syrian political and armed opposition factions have come together since the conflict erupted.
But another Russian deputy foreign minister, Mikhail Bogdanov, deplored that Ahrar al-Sham -- which is linked to Al-Qaeda's Syrian affiliate Al-Nusra -- and the rebel Jaish al-Islam (Army of Islam), had been invited to the Riyadh talks as they are "strongly suspected of being terrorist organisations".