Russian President Vladimir Putin met Saudi Arabia's defense minister on Sunday, in Moscow's biggest attempt so far to reach out to enemies of the Syrian government since Russia joined the conflict with airstrikes.

Speaking after the meeting between Putin and Sheikh Mohammed bin Salman, a son of the Saudi king, Russian Foreign Minister Sergei Lavrov said both countries were willing to cooperate in Syria and wanted to prevent the formation of a "terrorist caliphate".

"On both sides, as far as I can tell, there is an understanding that today's meeting can advance our cooperation," Lavrov said.