NATO chief Jens Stoltenberg warned on June 16 that a Russian plan to deploy 40 new nuclear ballistic missiles announced by President Vladimir Putin was part of a dangerous pattern of behavior by Moscow.
Stoltenberg, speaking after a meeting with European Commission head Jean-Claude Juncker in Brussels, said, "This nuclear saber-rattling by Russia is unjustified, destabilizing and it is dangerous."
Stoltenberg said Moscow's rhetoric explained the Western alliance's increased preparedness on the part of its forces to defend its members.
"We are responding by making sure that NATO also in the future is an alliance which provides the terms of protection of all allies against the enemy," he said.
NATO's commander for Europe, meanwhile, said the United States and other allies are considering placing heavy military equipment in the alliance's eastern flank nations.
General Philip Breedlove, speaking in Poland during NATO exercises, said Washington is "clearly" considering it, although the decisions and announcements haven't been made yet.
U.S. Secretary of State John Kerry, speaking separately in Washington, said he was concerned by Putin's announcement.
Following Stoltenberg's statement, Putin said that Russia would have to defend itself and direct its armed forces at any countries that might threaten it.
Earlier on June 16, Putin said the Russian military will add more than 40 new intercontinental ballistic missiles (ICBMs) to its arsenal this year capable of "penetrating" any current missile defense systems.
Putin said at the opening of the Army-2015 arms show in Moscow that the ICBMs are part of Russia's "large-scale armament- and defense-industry modernization program."
He said the military is also getting several other new weapons, including Armata tanks and new armored vehicles, several of which were on display during the military parade in Moscow's Red Square last month.