Russia will add more than 40 intercontinental ballistic missiles (ICBMs) to the country’s nuclear arsenal in 2015, President Vladimir Putin announced Tuesday amid tensions with the West over the conflict in eastern Ukraine. The move followed the United States’ proposal to increase its military presence in NATO states in Eastern Europe.

Speaking at the opening of the Army-2015 military show at a shooting range in Alabino, 33 miles west of Moscow, Putin said that Russia’s arms modernization would continue despite the nation’s economic downturn. The Russian leader also said that the military would begin testing a new long-range early warning radar, which would be deployed to monitor the country's western border, the Associated Press (AP) reported.

“Over 40 new intercontinental ballistic missiles capable of penetrating any, even the most technologically advanced missile defense systems, will join the nuclear forces in the current year,” AP quoted Putin as saying.

According to Russian defense minister Sergei Shoigu, the military received 38 ICBMs last year as part of the Kremlin’s efforts to modernize the country’s nuclear forces. Russian arms makers have also contributed toward the re-armament program, and have used the Army-2015 event to showcase costly new weapons, despite the country’s bleak economic outlook, which has been affected by Western santions.

During the show, the Russian navy reportedly revealed a project of an aircraft carrier, which can carry as many as 90 aircraft. The navy also demonstrated a mock-up of a new amphibious landing ship, which is similar to the France-made Mistral-class ship, whose delivery to Russian has been suspended over the crisis in eastern Ukraine.

The Russian military is currently estimated to have about 4,500 nuclear warheads, including nearly 1,800 strategic warheads deployed on missiles and at bomber bases, and 700 strategic warheads stored along with 2,700 non-strategic warheads. The country is also estimated to have nearly 3,500 retired, but largely intact, nuclear warheads ready to be dismantled, BBC reported.

Meanwhile, NATO Secretary-General Jens Stoltenberg accused Russia of unwarranted “nuclear saber rattling,” and said that the Russian arms buildup was “unjustified” and “dangerous.”

“This is something we are addressing, and it’s also one of the reasons we are now increasing the readiness and preparedness of our forces,” Reuters quoted Stoltenberg as saying. “We are responding by making sure that NATO also in the future is an alliance which provides deterrence and protection for all allies against any threat.”

U.S. Secretary of State John Kerry also expressed concern over Putin’s announcement, adding that the Russian president may be posturing over nuclear disarmament negotiations.

“It's really hard to tell,” AP quoted Kerry as saying. “But nobody should hear that kind of an announcement from the leader of a powerful country and not be concerned about the implications.”