MOSCOW (Reuters) - Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry have discussed the outlook for resuming stalled Syrian peace talks, the Russian foreign ministry said on Tuesday.

During the telephone conversation, Lavrov also said it was unacceptable for the Syrian opposition to set pre-conditions for the resumption of the negotiations.

Russia backs Syrian President Bashar al-Assad and has conducted airstrikes against various rebel groups who are battling government forces, including Islamic State.

(Reporting by Vladimir Soldatkin; Editing by Gareth Jones)