Talks between Washington and Pyongyang have been deadlocked since the collapse of a summit between Trump and North Korean leader Kim Jong Un in Hanoi in February when they failed to agree a deal on denuclearisation.

The North has since sought to raise the pressure and carried out two short-range missile tests earlier this month.

Bolton said Saturday there was "no doubt" they violated UN Security Council resolutions against ballistic missile launches, but insisted Washington was still ready to resume talks.

A spokesman for the North's foreign ministry dismissed Bolton's remarks, saying Pyongyang had never accepted the UN bans on ballistic technology, which denied its "rights as a sovereign nation".

"Bolton said our regular military drills violated UNSC resolutions, which is beyond stupid," he said in a statement carried by the official Korean Central News Agency (KCNA).

Without referring to the weapons as missiles, the statement said the launches did not target or threaten any neighbouring countries.

"Banning launches using ballistic technology is equal to telling us to give up our right to self defence," he added.

The spokesman went on to denounce Bolton, calling him a "war maniac" and accusing him of "whispering war" into Trump's ears, referring to Washington's approach towards the Middle East and South America.

Calling the hawkish official "structurally faulty", he added that Bolton was working to "destroy peace and security".

"Such human defect must go away as soon as possible," the spokesman said.

The statement came just minutes after Trump -- on a visit to Japan -- said there was "great respect" between the United States and North Korea and predicted "lots of good things".

Trump expressed confidence in his relationship with Kim at the weekend and downplayed Pyongyang's recent missile launches, calling them "small weapons" that "disturbed some of my people, and others, but not me".

Last week, KCNA launched a diatribe against Democratic former US vice president Joe Biden, calling him an "imbecile" and a "fool of low IQ", prompting White House spokeswoman Sarah Sanders to say that Trump agreed with the assessment.