In a joint declaration this week, NATO leaders criticised North Korea for "fuelling Russia's war of aggression against Ukraine" by "providing direct military support" to Moscow.

NATO leaders also voiced "profound concern" over China's industrial support for Russia.

Pyongyang has repeatedly denied allegations that it is shipping weapons to Moscow, but in June leader Kim Jong Un and Russian President Vladimir Putin signed an agreement that included a pledge to come to each other's military aid if attacked.

Pyongyang's Korean Central News Agency reported Saturday that the foreign ministry "most strongly denounces and rejects" the NATO declaration.

Citing a ministry spokesman, the agency said the declaration "incites new Cold War and military confrontation on a global scale", and requires "a new force and mode of counteraction".

On the sidelines of the NATO summit, Seoul and Washington this week also signed guidelines on an integrated system of deterrence for the Korean peninsula to counter North Korea's nuclear and military threats.

South Korea's presidential office said Seoul and Washington would carry out joint military drills to help implement the newly announced guidelines, which formalise the deployment of US nuclear assets on and around the Korean peninsula to deter and respond to potential nuclear attacks by Pyongyang.

In a separate statement released later Saturday, North Korea's defence ministry accused Seoul and Washington of harbouring the "intention to step up their preparations for a nuclear war against" the North by signing the guidelines.

That required the North to "further improve its nuclear deterrent readiness and add important elements to the composition of the deterrent", the statement said.

"If they ignore this warning," it added, the US and South Korea "will have to pay an unimaginably harsh price for it".

Relations between the two Koreas are at one of their lowest points in years, with Pyongyang ramping up weapons testing as it draws closer to Russia.

After Pyongyang sent multiple barrages of trash-carrying balloons across the border, Seoul last month fully suspended a tension-reducing military deal and resumed live-fire drills on border islands and near the demilitarised zone that divides the Korean peninsula.