Frustrated by months of failure in Syria, the U.S. is taking what might be its final offer to Russia.

Officials say Moscow would get long-sought intelligence and military cooperation to fight the Islamic State and other extremist groups, if Syria's Russian-backed leader upholds a ceasefire with U.S.-supported rebel groups and starts a political transition.

Secretary of State John Kerry, who will travel to Moscow later this week, has spoken of an August deadline for Syria's transition to begin.

Such a scenario appears highly unlikely, but U.S. options are limited.

The White House opposes a military intervention against Syrian President Bashar Assad's government.

The officials weren't authorized to speak publicly on internal American deliberations and demanded anonymity.