UNITED NATIONS: Iran's president said Sunday that Syrian leader Bashar Assad must remain in power to fight extremist groups like ISIS and must not be weakened, putting him at odds with the United States and key nations who insist Assad must go in order to achieve peace.

Hassan Rouhani told a meeting with scholars and think tank experts that Iran will cooperate with any country that puts fighting and defeating "terrorism" as its top priority - but he said it cannot work with any government that makes a change in Syria's regime its top priority.

He said the Syrian government does need reform. But he warned that if getting rid of Assad is the top goal, as soon as that happens "the terrorists will enter Damascus immediately" as well as other cities controlled by the government, and all will fall to ISIS.

Rouhani's comments run counter to the road-map to peace in Syria adopted by key nations in Geneva in June 2012. It calls for the formation of a transitional government with full executive powers "on the basis of mutual consent," leading to elections, and would require Assad to relinquish power at some unspecified point.

The Iranian president's remarks came on the eve of the annual meeting of world leaders at the United Nations, where frustration is growing at the failure to launch talks to end the nearly five-year-old Syrian war. They also follow a surprise Russian military buildup in Syria, a longtime ally, to help Assad's government combat the ISIS, a move that has raised serious concerns in Washington. And they came on the heels of France's announcement earlier Sunday that it had carried out airstrikes in Syria for the first time, bombing an ISIS training camp in eastern Syria.

Rouhani said he recently met Russian officials who told him that they wanted to enter the Syrian "scene" with a renewed determination to fight "Daesh and terrorists." He added that "Iran and the Russians have an almost compatible mindset and opinion about this because they have the same goal of fighting and defeating terrorism."

ISIS already controls about two-thirds of Syria, and "has had the greatest safe havens and growth opportunities" in the country, he stressed.

"If we are to succeed in defeating terrorism, the government in Damascus cannot be weakened," Rouhani stressed. "It must be able to carry on the fight."

Rouhani said "the West's opinion about Syria has changed somewhat in recent months" and the insistence that Assad must leave "no longer has that many fans." But he said there is still no agreement on how to proceed.

The Iranian leader also said it is not feasible to fight "terrorists" by military means, using helicopter gunships, missiles or aerial bombardments because they go into the heart of villages, in rural areas and in homes and "they fool people."

Months ago Iran produced a proposal to end the Syrian conflict, which has claimed more than 250,000 lives, and Rouhani said it is still under discussion with some unnamed countries.