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