North Korea has taken the unusual step of sending a letter to other countries, with the Australian prime minister describing it "a rant about how bad Donald Trump is".

Australia's Sydney Morning Herald published the letter, with officials in the country verifying it.

In the 'Open Letter to Parliaments of Different Countries', the secretive state writes: "Trump threatened to totally destroy the DPRK, a dignified independent and soverign state and a nuclear power. it is an extreme act of threatening to totally destroy the whole world."

"If Trump thinks that he would bring the DPRK, a nuclear power, to its knees through nuclear war threat, it will be a big miscalculation and an expression of ignorance."

Malcolm Turnbull, the Australian prime minister, indicated that the letter was sent to "a lot of other countries".

He told radio station 3AW that it was "basically a rant about how bad Donald Trump is", adding that he believed North Korea was starting to 'feel the squeeze' due to global sanctions.

Australia's foreign minister Julie Bishop noted it was an "unprecedented" communication, and "not the way [North Korea] usually publish their global messages".

Recent months have seen a war of words between North Korea and the US, with Donald Trump describing the North Korean leader as a "rocket man" on a suicide mission.

North Korea, meanwhile, has hit out at President Trump as an "old lunatic".

The secretive state has drawn international condemnation for its missile & nuclear tests.