Russia's Foreign Minister Sergei Lavrov on Friday urged the UN's special envoy on Syria to include Kurds in upcoming talks that aim to resolve the five-year Syrian civil war.
"I am convinced that Staffan de Mistura should take such a decision," Lavrov told reporters at a joint news conference with his Chinese counterpart.
"Launching negotiations without the participation of this group would be a sign of weakness from the international community," Lavrov said.
Russia's top diplomat argued that holding talks on forming a new ruling structure in Syria to prepare constitutional reform and elections without Kurds would be "a most serious infringement of the rights of a large and significant group living in Syria."
Kurds are "allies both of the US coalition and Russia" and control at least 15 percent of Syrian territory," Lavrov added.
Lavrov hit out at Turkey, saying that "only Turks are blocking the invitation of Kurds from the Syrian Kurdish Democratic Union Party (PYD)," criticising this as "an ultimatum."
Turkey accuses the PYD of being the Syrian branch of the outlawed Kurdistan Workers Party (PKK).
The issue of the Syrian Kurds has caused a rare rift between Ankara and Washington.
The United States regards the armed wing of the PYD as the most effective fighting force on the ground against Islamic State jihadists and has resisted Turkish pressure to classify the group as a terror organisation.
De Mistura told Russian state news agency RIA Novosti Friday that "we are not sending out new invitations" to the upcoming talks, in response to a question on broadening opposition participation.
At the same time, in comments translated into Russian, he stressed the importance of "ensuring as far as possible inclusiveness and participation of all Syrians who can make a contribution to Syria's future."
The UN is hoping to restart peace talks that collapsed last month, building on a ceasefire that has led to the first significant decline in violence in Syria's nearly five-year civil war.
A new round of talks aimed at ending the war in Syria will begin in Geneva on March 14 and will last no longer than 10 days, the UN mediator has said.