MOSCOW — World leaders will be able to secure a peace deal in Syria only if Washington drops demands for President Bashar Assad's removal and the threat of airstrikes, an ally of President Vladimir Putin said.

Russia, Assad's main backer, has portrayed itself as the peacemaker in Syria since winning Washington's support for a proposal that Damascus give up its chemical arms to avert U.S. military intervention over a poison gas attack.

Alexei Pushkov, head of the lower house of parliament's foreign affairs committee, said he hoped the agreement could become the springboard to reaching a peace deal.

But he said this would depend on the U.N. Security Council agreeing on a resolution to enforce it and Washington abandoning what he called an ideology based on "regime change."

"The world is now praising Russia for giving this way out of a potential military conflict, and looking suspiciously at Washington and what it will decide," Pushkov told the Reuters Russia Investment Summit on Tuesday night. "Will they prefer the peaceful diplomatic, political option, or the military option?"

Russia proposed that Syria give up its chemical arms after Washington threatened to strike Syrian targets following an Aug. 21 gas attack which the United States blames on Assad's forces and which Moscow says was probably carried out by rebel forces.

The United States accepts the proposal but disagrees with Moscow on whether the Security Council resolution enforcing the deal should include an automatic threat of sanctions or the use of force in the case of non-compliance.

"If we reach this chemical agreement with Washington, London and Paris, then it can have a future and become a political agreement," Pushkov said. "If it remains just the lowest common denominator but all the goals outside of it are completely different, then I don't think it will be conducive to a peace agreement — because the goals outside of the chemical agreement remain very different."

Pushkov, 59, holds no policy-making powers but has aligned himself closely with Putin's stance on Syria and become one of Russia's fiercest critics of U.S. foreign policy, at times provoking anger and criticism in the United States.

Although he is seen in Washington as a hawk and the United States has long regarded Russia as an obstacle to peace in Syria, Pushkov made clear Moscow was wary of U.S. intentions.

"I hope that the political process prevails but I think the military temptation will be always on the table [for the United States], which makes the whole situation extremely difficult and dangerous," Pushkov said. "There is a war party that wants war, no matter what Assad does. . . . The war party in Washington is pretty influential."

If agreement is reached on enforcing the chemical arms deal, the next step towards ending the civil war in Syria is likely to be an international peace conference which Washington and Moscow are trying to arrange.

Pushkov said its success would depend on the United States doing more to bring the rebels to the negotiating table.

"If you talk to them in the right way, they will come. Because they will not have any other option — otherwise they may lose their support. The question is whether the United States want them to come or not," Pushkov said.

Western powers believe Assad's exit is vital for any negotiated peace settlement in Syria but Russia has said it must not be a pre-condition for talks.

He said officials with experience of running the country would be needed to help provide stability after a peace deal is reached and warned that chaos would follow — as after Libya's civil war — if militant Islamists won power.

"You have to have running water. Will the head of the Free Syrian Army do this?" Pushkov asked. "The governing structures should be conserved, you cannot do it without conserving at least part of the government."