MOSCOW — Russia said Friday 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 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 currently 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 Friday that 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.

The normal supply route to landlocked Afghanistan via Pakistan has come under repeated Taliban attack, and the U.S. and NATO have been eager to have an alternate overland supply route through Russia and the Central Asian countries.

Confirmation of such a deal appeared aimed at setting a constructive tone for the meetings between Obama and Russian President Dmitry Medvedev on Monday and Tuesday. After years of increasing strain, both governments have expressed hope the summit will put ties between the former Cold War rivals back on track.

Military analyst Alexander Golts, however, said the U.S. should be under no illusion about Russia's intentions. Although Medvedev has set a warmer tone in relations with the West, his predecessor, Vladimir Putin, retains considerable power as prime minister.

"The least impression you should get from this is that Putin's foreign policy style foresees gestures of goodwill," Golts said.

The Russian leadership still has the mindset of "19th-century Realpolitik" and seeks the ability to hold its partners "by the throat," he said.

"If something goes wrong in Russian-U.S. relations, this transit will cease as quickly and suddenly as it started," Golts said.

While Russia has stressed a willingness to work with the West to bring stability to Afghanistan, it has shown that it can use its clout in the former Soviet republics of Central Asia to hobble U.S. efforts.