Stoltenberg welcomed the meeting planned for Friday between North Korean leader Kim Jong Un and the South's president Moon Jae-in but said there should be no let up yet in pressure on Pyongyang.

"Until we see a concrete change in North Korea's actions we must continue to put pressure on North Korea and continue with the sanctions," Stoltenberg told reporters at NATO headquarters in Brussels.

Friday's meeting at the line that divides the Korean peninsula will be only the third of its kind, following summits in Pyongyang in 2000 and 2007.

Stoltenberg said the summit, which comes ahead of a much-anticipated meeting between Kim and US President Donald Trump, was "a first important step towards a negotiated peaceful solution to the crisis on the Korean peninsula".

"One of the reasons why we see the progress we have seen over recent weeks is because there has been strong pressure on North Korea, not least by sanctions that the UN has adopted," Stoltenberg said.

"I welcome both that UN has been able to agree on stricter sanctions on North Korea but also that we have seen that they have been implemented to a higher degree than before."

The tension-wracked peninsula has seen a dramatic diplomatic rapprochement in recent weeks, since Moon used the South's Winter Olympics as an opportunity to broker dialogue with Pyongyang.