North Korea says it is 'ready for war' with Donald Trump's United States

'The nuclear force of [North Korea] is the treasured sword of justice and the most reliable war deterrence'

North Korea has declared it is ready for war with the United States and does not fear possible preemptive military action to halt its nuclear and missile buildup.

Comments from North Korea's foreign ministry slammed US Secretary of State Rex Tillerson's recent talk of tougher sanctions, more pressure and possible military action, and said the north would not be deterred in its nuclear program.

"The nuclear force of [North Korea] is the treasured sword of justice and the most reliable war deterrence to defend the socialist motherland and the life of its people," the official Korean Central News Agency quoted the spokesman as saying.

"We have the will and capability to fully respond to any war which the US wants. If the businessmen-turned-US officials thought that they would frighten us, they would soon recognise that their method would not work."

The comments come after US President Donald Trump rebuked North Korean leader Jim Jong-un for "acting very badly" after it conducted a ground test for a new type of high-thrust rocket engine.

The North Korean leader called it a revolutionary breakthrough for the country's space program.

Last week, Mr Tillerson signalled a tougher strategy and left open the possibility of preemptive military action against the North.

"Let me be very clear: The policy of strategic patience has ended," he said after visiting the heavily militarised border between the rival Koreas.

"We are exploring a new range of diplomatic, security and economic measures. All options are on the table."

Tensions have worsened after a series of ballistic missile tests as the North attempts to miniaturise a nuclear warhead able to be mounted on an inter-continental ballistic missile.

North Korea has accelerated its weapons development, violating multiple UN Security Council resolutions without being deterred by sanctions.

It conducted two nuclear test explosions and 24 ballistic missile tests last year. Experts warn it could have a nuclear-tipped missile capable of reaching the US mainland within a few years.