The recent US extension of sanctions against North Korea was an act of hostility and an outright challenge to an historic summit between the two countries in Singapore last year, a spokesman for Pyongyang's foreign ministry said today.

The White House last week extended six executive orders containing sanctions imposed over North Korea's nuclear and missile programmes by one year.

The unidentified North Korean foreign ministry spokesman denounced US Secretary of State Mike Pompeo's remarks on Sunday that more than 80 per cent of the North Korean economy has been affected by sanctions.

The spokesman also accused Washington of "viciously slandering" Pyongyang in its latest reports on human trafficking and religious freedom around the world.

"This is ... a manifestation of the most extreme hostile acts by the United States," the spokesman said in a statement carried by the North's official KCNA news agency.

"All these speak clearly to the fact that the wild dream of the United States to bring us to our knees by means of sanctions and pressure has not changed at all but grows even more undisguised," he added.

US President Donald Trump and North Korean leader Kim Jong Un held their first, groundbreaking summit in Singapore in June last year, agreeing to foster new relations and work towards the denuclearisation of the Korean peninsula.

But a second summit in Vietnam in February collapsed as both sides failed to bridge differences between US calls for denuclearisation and North Korean demands for sanctions relief.

Since then, North Korea has complained of US sanctions and demanded Pompeo be replaced by someone "more mature", while lauding the rapport Kim built with Trump.

Pompeo, speaking to reporters on Sunday, raised hopes for a revival of nuclear talks after a recent exchange of letters between Trump and Kim.

The North Korean spokesman warned it would be difficult to achieve denuclearisation as long as US politics are dominated by policymakers who have an "inveterate antagonism" towards North Korea.

"We would not thirst for a lifting of sanctions," the spokesman said.

"Our state is not a country that will surrender to the US sanctions, nor are we a country which the US could attack whenever it desires to do so," he