Washington  - US President Barack Obama said Wednesday he backs the expansion of NATO to European countries aspiring to join the alliance but pledged to work towards reinvigorating US-Russian relations.

Obama, meeting with NATO Secretary General Jaap de Hoop Scheffer just a week before the alliance summit, also said he will present his administration's strategic review of the situation in Afghanistan to other members.

NATO's struggling mission in Afghanistan will be at the top of the agenda during the April 3-4 summit in Germany and France to celebrate the alliance's 60th anniversary.

"We believe that we are going to be able to ensure that the NATO members who make so many sacrifices and have been working so hard already are reinvigorated," Obama said.

De Hoop Scheffer called Afghanistan NATO's "most important operational priority" as it continues to fight against resurgent Taliban militants.

"In Afghanistan there are still major challenges. Many things are going right, but many things are not going right," de Hoop Scheffer said.

Moscow has strongly opposed NATO's expansion closer to its borders, particularly NATO's agreement last year to eventually offer membership to Georgia and Ukraine, two former Soviet states. Obama did not mention the two countries.

"My administration is seeking a re-set of the relationship with Russia, but in a way that's consistent with NATO membership and consistent with the need to send a clear signal throughout Europe that we are going to continue to abide by the central belief that countries who seek and aspire to join NATO are able to join NATO," Obama said.

A larger NATO has been one of many sources of tension between the United States and Russia. Another has been US plans initiated by former president George W Bush's administration to base a missile- defence system in Poland and the Czech Republic to counter Iran's growing ballistic missile capabilities.

Obama has sent a letter to Russian President Dmitry Medvedev suggesting he's willing to back off or delay the deployment if Moscow takes a tougher stance to rein in Iran's nuclear activities.

De Hoop Scheffer said NATO and Russia must continue building a cooperative relationship even as the two sides disagree on some issues.

"We have many things on which we disagree, but NATO needs Russia and Russia needs NATO," de Hoop Scheffer said. "So let's work on the things we agree on, and let's not hide our disagreements, and let us realize that also this relationship can, and in my opinion, should be strengthened."

Obama has announced plans to send an additional 17,000 troops to Afghanistan this year, bringing the American presence to more than 50,000 soldiers. During the summit, Obama is expected to press reluctant allies to contribute more in Afghanistan. (dpa)