In a joint statement with the United States, Britain, France, Germany and Gulf Arab allies, Turkey said Russia's actions constituted a "further escalation" of the conflict and would only fuel more extremism.

"We express our deep concern with regard to the Russian military build-up in Syria and especially ‎the attacks by the Russian Air Force on Hama, Homs and Idlib since yesterday which led to civilian casualties and did not target Daesh," it said.

Daesh is another name for the Islamic State group. Russian President Vladimir Putin said on Thursday assertions that civilians had been killed in Russian air strikes in Syria were an "information attack".

Russia's decision to join the war with air strikes on behalf of Syrian President Bashar al-Assad this week, and the increased military involvement of Iran, could mark a turning point in a conflict that has drawn in most of the world's military powers.

Hundreds of Iranian troops have arrived in Syria to join a major ground offensive in support of Assad's government, Lebanese sources said on Thursday, a sign the civil war is turning still more regional and global in scope.

(Reporting by Humeyra Pamuk; Editing by Catherine Evans)