President Vladimir Putin has defended Russia's military operations in Syria, saying the aim is to "stabilize the legitimate authority" of Syrian President Bashar al-Assad.
Mr. Putin told Russian state TV Moscow also wanted to "create conditions for a political compromise" in Syria.
He denied that Russian air strikes were hitting moderate opposition groups rather than Islamic State militants.
Syrian forces are said to have made significant advances against rebels.
Government gains in Idlib, Hama and Latakia provinces were on Sunday reported both by Damascus and opposition activists.
The main battlefront is currently close to the key highway that links the capital with other major cities, including Aleppo, and Mr Assad's forces are believed to be seeking to cut off rebels in Idlib.