Russian President Vladimir Putin attends a session of the Valdai International Discussion Club in Krasnaya Polyana, Sochi, Russia, October 22, 2015. REUTERS/Alexander Zemlianichenko/Pool

SOCHI, Russia (Reuters) - The expansion of the United States’ ballistic missile defense system is a threat to Russia’s nuclear capability, Russian President Vladimir Putin said on Thursday.

Putin added that U.S. ballistic missile shield bases in Eastern Europe could also be used to station offensive weapons and that he was worried about NATO military infrastructure moving closer to Russia’s borders.