MOSCOW — Russia said today it will allow the United States to ship weapons across its territory to Afghanistan, a long-sought move that bolsters U.S. military operations.

But it also potentially gives the Kremlin leverage over critical American supplies.

The announcement by a top Kremlin aide came ahead of President Barack Obama's visit to Moscow next week, when the deal is expected to be signed during a summit aimed at improving the nations' strained relations.

Russia's concession on arms shipments also came as the Obama administration is shifting the U.S. military's focus from Iraq to Afghanistan, where a massive American offensive is under way in Taliban-controlled areas of Helmand province.

Russia has been allowing the United States to ship non-lethal supplies across its territory for operations in Afghanistan, and Kremlin officials had suggested further cooperation was likely.

Kremlin foreign policy adviser Sergei Prikhodko told reporters today the expected deal would enable the U.S. to ship lethal cargo and would include shipments by air and land.

He said it was unclear if U.S. soldiers or other personnel would be permitted to travel through Russian territory or airspace.

"They haven't asked us for it," he said.