UN envoy Staffan de Mistura was due to send out invites Tuesday to opposition groups to attend the talks after negotiations were delayed several days to Friday due to a "stalemate" over the makeup of the delegations.
Lavrov said that one of the international powers backing the Syria talks -- most likely meaning Turkey -- was objecting to the participation of the Kurds and the Syrian Kurdish Democratic Union Party (PYD) in particular.
"Without this party, without this participant the talks cannot achieve the results that we want, a definitive political resolution in Syria," Lavrov told journalists at his main annual press conference.
Lavrov said, however, that Russia would not "veto" the talks if the Kurds were not invited and that it was up to the UN envoy de Mistura to decide which opposition groups would be asked to attend.
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Turkey, which has condemned the PYD, has said that it wants to see some Syrian Kurds "around the table" at the talks.
Turkey considers the PYD to be the Syrian offshoot of the outlawed Kurdistan Workers' Party (PKK), which has waged a bloody insurgency in the mainly Kurdish southeast of Turkey since 1984.
Last month, several key opposition bodies, including rebel groups, formed a coalition known as the High Negotiations Committee to participate in the mooted talks.
But the coalition excludes Syria's main Kurdish party the PYD and a range of other opposition figures.
Ties between Russia and Turkey are in tatters over the shooting down last year of one of Moscow's jets by Ankara along its border with Syria.
Russia has been running a bombing campaign in Syria since last September in support of its longstanding ally President Bashar al-Assad, who is fiercely opposed by Turkey.