Syrian President Bashar al-Assad arrived for talks in Tehran on Saturday, a few weeks after he told France he would use his good relations with Iran to help resolve its nuclear stand-off with the West.
Assad's two-day visit to Iran coincides with an informal deadline set by Western officials in the dispute over Tehran's atomic plans, which the United States suspects are aimed at making bombs. The Islamic Republic says its aims are peaceful.
Syria's president was expected to meet his Iranian counterpart Mahmoud Ahmadinejad and other senior officials.
That would suggest a deadline of Saturday, although Russia, one of the six powers facing Iran, has opposed a deadline and Iran dismissed the idea of having two-weeks to reply.
Visiting Paris last month, Assad said he would respond to French President Nicolas Sarkozy's request and use his good ties with Iran to help resolve the nuclear row.
He also said in the French capital on July 14 that a military attack on Iran over its nuclear programme would have grave consequences for the United States, Israel and the world.
The United States, China, Russia, Britain, France and Germany in June offered Iran economic and other incentives to coax it into halting uranium enrichment, which can have both civilian and military uses.
Iran has said that it has rights on nuclear program like every country and rejected suspension in the past and has given no indication that it is ready for a freeze.
Assad was expected to meet Iranian President Mahmoud Ahmadinejad and other senior officials during a two-day visit.