TEHRAN: Russia's President Vladimir Putin was in Tehran on Monday for talks with Iranian leaders expected to focus on the Syrian crisis and an international peace plan intended to end the conflict.

The visit comes as Russia, the United States, France and others are talking about possible joint action against the Islamic State group following the terror attacks in Paris and the downing of a Russian passenger jet in Egypt. Putin's trip also comes on the heels of agreement on an incomplete peace plan that calls for talks between Assad and his foes.

Moscow and Tehran have been the key backers of Syrian President Bashar Assad throughout his nation's civil war, which has killed over 250,000 people and turned millions into refugees.

Russia has shielded Syria from international sanctions, and on Sept. 30 it launched an air campaign against the Islamic State group and other insurgents, while Tehran has sent military advisers to shore up Assad.

Putin, on a one-day visit to attend a gas exporting nations' summit, is set to meet with Iran's Supreme Leader Ayatollah Ali Khamenei and President Hassan Rouhani. Assad's fate will likely dominate the agenda.

The peace plan put forward by 17 nations a day after the Paris terror attacks sets a Jan. 1 deadline for the start of negotiations between Assad and the opposition.

The proposal, which seems to draw heavily on a recently circulated Russian initiative, states that "free and fair elections" would be held according to a new constitution within 18 months. To clarify the timeline, the State Department said last week that the clock starts once Assad's representatives and opposition figures begin talks on a constitution. The vote would determine a new parliament, though not necessarily a new president.

The plan says nothing about Assad's fate, and does not say which of Syria's many opposition factions would take part in the negotiations.

Russia and Iran both have bristled at demands for Assad to step down, saying his future must be decided by the Syrians as part of the peace process. But some have speculated that Moscow could be prepared to see Assad phased out of power as part of a deal that would guarantee stability in Syria and protect Russia's interests there. Tehran is widely seen as taking a more rigid stance.

Shiite Iran has staunchly backed Assad, who belongs to Syria's Alawite minority, an offshoot of Shiite Islam, seeing him as a bulwark against its archrival, Saudi Arabia, and other Sunni monarchies of the Gulf. Tehran has sent more advisers to Syria in recent weeks, reportedly including Gen. Qassem Soleimani, who heads the elite Quds Force of the Revolutionary Guard. Iran says it has sent advisers but no combat forces.

Taking advantage of the Russian airstrikes, the Iranians and Hezbollah have spearheaded the ongoing Syrian offensive intended to win back some ground after a string of losses earlier this year. Moscow has closely coordinated its air campaign with Tehran, with Russian warplanes flying over Iran and Iraq to avoid the airspace of Turkey and other NATO members.