Jens Stoltenberg. NATO secretary

Nato has condemned Russia’s move to strengthen its nuclear arsenal, saying it amounted to “nuclear sabre-rattling” and was “unjustified” and “dangerous”.

President Vladimir Putin said Russia would put more than 40 new intercontinental ballistic missiles into service this year.

It is part of a wide-reaching program to modernize the country’s military.

The move comes after the US proposed increasing its military presence in Nato states in Eastern Europe.

Tensions are high over Russia’s role in the conflict in eastern Ukraine.

Nato Secretary-General Jens Stoltenberg said that the statement from Mr Putin was “confirming the pattern and behaviour of Russia over a period of time – we have seen Russia is investing more in defence in general and in its nuclear capability in particular”.

He said: “This nuclear sabre-rattling of Russia is unjustified, it’s destabilising and it’s dangerous.

“This is something which we are addressing and it’s also one of the reasons why we now are increasing the readiness and the preparedness of our forces.”

He added that “what Nato now does in the eastern part of the alliance is something that is proportionate, that is defensive and that is fully in line with our international commitments”.

US Secretary of State John Kerry also expressed concern over President Putin’s announcement, saying the decision was in contravention of the Start agreement designed to destroy nuclear weapons in the former territories of the Soviet Union.

“It could well be posturing with respect to negotiations because of their concerns about military moves being made by Nato itself,” he said.

But “nobody should hear that kind of announcement from the leader of a powerful country and not be concerned about what the implications are,” he added.