North Korea has said it will defend itself "by powerful force of arms" in response to the US deployment of a Navy strike group to the Korean peninsula.

The foreign ministry, quoted by state news agency KCNA, said the deployment showed "reckless moves for invading" had "reached a serious phase".

The US Pacific Command says it is aimed at maintaining readiness in the region.

President Trump has said the US is prepared to act alone to deal with the nuclear threat from North Korea.

The Carl Vinson Strike Group comprises an aircraft carrier and other warships. It was due to make port calls in Australia but instead has been diverted from Singapore to the west Pacific, where it recently conducted exercises with the South Korean Navy.

"We will hold the US wholly accountable for the catastrophic consequences to be entailed by its outrageous actions," said the foreign ministry statement quoted by KCNA.

"The DPRK is ready to react to any mode of war desired by the US," the statement said.

The US naval deployment showed North Korea had been right to develop nuclear weapons capability for use in self defence or in a pre-emptive strike, the statement added.

North Korea has carried out several nuclear tests and experts predict more could be in the offing as it moves closer towards developing a nuclear warhead that could reach the US.

There have been indications from North Korea that it may test an intercontinental missile, even though it is banned from any tests under UN resolutions.

North Korea says it is provoked by military exercises between the US and South Korea, which it sees as preparation for an invasion.