Secretary of State John Kerry said Tuesday that the Obama administration hopes Russia and Iran will play a positive role in Syria and back a political transition for the country to end the current conflict and blunt the Islamic State group.

Kerry said Russian and Iranian support for Syrian President Bashar Assad is misplaced and will only prolong the war. But he said the U.S. is ready to engage in an immediate dialogue with Russia to promote a peace agreement that would see Assad removed from power.

He said that Russia's military buildup in Syria appears initially intended to protect its existing assets and personnel on the ground. He added, though, that Moscow's ultimate aim in Syria is not yet clear. Russia has ferried weapons, troops and supplies to an airport near the Syrian coastal city of Latakia in what the U.S. sees as preparations for setting up an air base there.

Retired Army Gen. David Petraeus, a former commander in Iraq and Afghanistan, told the Senate Armed Services Committee on Tuesday that while Putin wants to shore up Assad, his thinks Putin's immediate objective in Syria is to solidify a corridor on the Mediterranean coast between Latakia, home to a Russian air base, and Tartus where there is a Russian naval base — the only naval base left in the Mediterranean.

Petraeus said, however, that the U.S. should not allow Moscow to push America into a partnership with Russia and the Iran-backed Assad to battle IS. If Russia wanted to fight IS extremists, it could have joined the more than 60-member coalition and help with airstrikes against the militant group, he said. He also warned that the U.S. should not rush to oust Assad without an understanding of who would seek to run the country.

Petraeus also said he does not think Putin is "playing the strongest hand in the world." He said Russia has an estimated $200 billion in foreign reserves and is expected to "burn through those" in a few years. If economic sanctions against Russia remain in place, Petraeus said Putin will have a hard time going to world markets to get the money to finance Russian debt.

"So I think he has actually a limited window of a couple of years to continue provocative actions in Ukraine, Belarus, Moldova, Syria, Georgia and so forth, and we have to be very careful during this time, when he could actually lash out and be even more dangerous than he has been," Petraeus said.

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Associated Press writer Deb Riechmann contributed to this report.