Concerned about Russia's growing tactical nuclear weapons, the United States will expand its nuclear capabilities, a policy document released on Friday said, a move some critics say could increase the risk of miscalculation between the two countries.

It represents the latest sign of hardening resolve by President Donald Trump's administration to address challenges from Russia, at the same time he is pushing for improved ties with Moscow to rein in a nuclear North Korea.

The focus on Russia is in line with the Pentagon shifting priorities from the fight against Islamist militants to "great power competition" with Moscow and Beijing.

"Our strategy will ensure Russia understands that any use of nuclear weapons, however limited, is unacceptable," the document, known as the Nuclear Posture Review, said.

The rationale for building up new nuclear capabilities, US officials said, is that Russia currently perceives the United States' nuclear posture and capabilities as inadequate.

Russia's Foreign Ministry yesterday said in a statement it was very disappointed by the content of the document, which, it said, has a confrontational feel and anti-Russian orientation.

Low-yield nuclear weapons, while still devastating, have a strength of less than 20 kilotons. The atomic bomb dropped on Hiroshima had about the same explosive power.

The argument for these weapons is that larger nuclear bombs are so catastrophic that they would never be used and do not work as an effective deterrent. With less power and destruction, the low-yield option would potentially be more likely to be used, serving as an effective deterrent.