VLADIVOSTOK, Russia: Russian Prime Minister Vladimir Putin said yesterday that US plans for a missile defense system were the main obstacle to reaching a new deal on reducing Cold War arsenals of nuclear weapons.

The two largest nuclear powers say they are close to agreeing on a successor to the 1991 Strategic Arms Reduction Treaty (START I), although US President Barack Obama and Russian President Dmitry Medvedev have yet to clinch a deal.

Asked by a reporter what the biggest problem was in the talks, Putin said: "What is the problem? The problem is that our American partners are building an anti-missile shield and we are not building one."