Russia's President Vladimir Putin is visiting Tehran for talks with the Iranian leadership expected to focus on the Syrian crisis.

Moscow and Tehran have been the key backers of Syrian President Bashar Assad throughout his nation's civil war. Russia has shielded Syria from international sanctions and on Sept. 30 launched an air campaign against the Islamic State group and other militants, while Tehran has sent military advisers to shore up Assad.

Putin is in Tehran Monday for a gas exporting nations' summit, and is set to meet with Iran's Supreme Leader Ayatollah Ali Khamenei and President Hassan Rouhani.

The talks are expected to focus on an international peace plan for Syria that sets a Jan. 1 deadline for the start of talks between Assad and his foes.