US President Barack Obama on Monday won Russian support for the war in Afghanistan with a breakthrough agreement allowing a dozen flights a day to transit US troops and weapons over Russian territory.

"This is a substantial contribution by Russia to our international effort," Obama said at a joint press conference at the Kremlin with Russian President Dmitry Medvedev.

Underscoring the deal''s strategic value for Russia, Medvedev said: "We value the efforts by the United States and other countries to deal with the terrorist threat that came from and continues to come from Afghan soil."

The deal marks a victory for Obama as he seeks to intensify the faltering campaign against the Taliban and "reset" US-Russian relations that were badly strained under his predecessor, George W. Bush.

It allows the use of Russian airspace for the transit of US troops and weapons. Previously Russia had only allowed the United States to ship non-lethal military supplies across its territory by train.

The need to diversify transit routes into Afghanistan has become more acute in recent months because of instability in Pakistan, which currently serves as the main transit route into the war-torn country.

The agreement was signed by Russian Foreign Minister Sergei Lavrov and US Undersecretary of State William Burns, who was standing in for Secretary of State Hillary Clinton as she recuperated from an elbow injury.