North Korea has said it has carried out another “crucial test” at its long-range rocket launch site.

The country’s Academy of Defence Science did not specify what was tested on Friday.

Earlier this week, Pyongyang said it carried out a "very important test" at the site – prompting speculation that it involved a new engine for either a space launch vehicle or an intercontinental ballistic missile.

The announcement comes as the country continues to pressure US President Donald Trump over a deadline set for the end of the year by leader Kim Jong Un to salvage faltering nuclear negotiations.

Negotiations broke down when the two men met at a Vietnam in February after the US rejected demands by North Korea for a relief on sanctions in exchange for a partial surrender of its nuclear capabilities.

A further meeting in October ended in deadlock over what North Korea called America's “old stance and attitude.”

North Korea has conducted 13 rounds of ballistic missile and rocket artillery tests since May and has hinted at lifting its moratorium on nuclear and long-range missile tests if the Trump administration fails to make substantial concessions.

Relations between the two countries have become ever more strained in recent weeks with North Korea threatening to renew its insults at Mr Trump.

The North said it would consider him a "dotard" if he keeps using provocative language against Kim Jong Un.

The country's foreign ministry issued the warning days after the US president spoke of possible military action and revived his "rocket man" nickname for the North Korean ruler.