Russian President Vladimir Putin said on Monday that Moscow would respond if the North Atlantic Treaty Organization (NATO) would deploy military infrastructure on the territories of Finland or Sweden.

"The expansion of military infrastructure into these territories would certainly trigger our response, which would depend on the kind of threats this would pose for us," the Kremlin cited the president as saying at a summit of the Collective Security Treaty Organization in Moscow.

Putin added that the issue of NATO enlargement is largely artificial, and is being used by the United States as a foreign policy tool.

"NATO is being used as a foreign policy instrument by one country, and this is being done quite persistently, skillfully and very aggressively," Putin said, further pointing out that the situation has a deteriorating effect on international security.

Both Finland and Sweden have announced decisions to apply for the NATO membership.

On Sunday, Finland's president and the government's foreign policy committee took the official decision to start the process of the country's application to become a NATO member. Swedish Prime Minister Magdalena Andersson announced on Monday the official decision to start the process of the country's application to become a NATO member.