They called him "bereft of elementary quality as a human being."

The criticism contrasts with North Korea's repeated references to the good relationship between Kim and U.S. President Donald Trump. Kim said in April his personal relationship with Trump was still good despite the collapse of their second summit in Vietnam in February.

According to Newsweek, Biden said at a campaign launch in Philadelphia on Saturday: "Are we a nation that embraces dictators and tyrants like (Russian President Vladimir) Putin and Kim Jong-un?"

State media the Korean Central News Agency (KCNA) responded to criticism of the North's leadership in a commentary late on Tuesday.

"What he uttered is just sophism of an imbecile bereft of elementary quality as a human being, let alone a politician," it said.

KCNA listed previous controversies concerning Biden, including allegations of plagiarism and falling asleep during a speech by former President Barack Obama in 2011.

"We will never pardon anyone who dare provoke the supreme leadership of the DPRK but will certainly make them pay for it," KCNA said, using North Korea's official name, the Democratic People's Republic of Korea.

Denuclearisation talks have stalled since the breakdown of the second meeting between Trump and Kim in February and North Korea conducted more weapons tests this month.

The tests were seen as a protest by Kim after Trump rejected his calls for sanctions relief at the Hanoi summit.