The Pentagon on Friday proposed to build new, smaller atomic bombs to counter Russia, as its current arsenal is too catastrophic to be used – and hence, no more an effective deterrent. The United States is concerned about Moscow’s growing tactical nuclear weapons, Reuters reported.

“Our strategy will ensure Russia understands that any use of nuclear weapons, however limited, is unacceptable,” a policy document, “Nuclear Posture Review”, by the US Department of Defense said.

The US wants to build new nuclear arsenal because Russia currently perceives its nuclear capabilities as inadequate, officials told Reuters. Low-yield nuclear weapons could help the US deter Russia more, officials said.

Low-yield nuclear weapons are also devastating but have a strength of less than 20 kilotons. The atomic bomb dropped on Nagasaki in August 1945 during the World War II had a similar explosive power.

This is the first time since 2010 that the US military has outlined its perception of future nuclear threats, the BBC reported.

In the long term, the US military also plans to develop a new nuclear-armed sea-launched cruise missile.

The Pentagon says Russia has a stockpile of 2,000 non-strategic nuclear weapons. The US has a few hundred active low-yield weapons deployed in Europe.