"At this moment, our official position is that we cannot confirm reports that North Koreans are actively now as soldiers engaged in the war effort," Rutte told reporters following a meeting of NATO defence ministers in Brussels.

"But this, of course, might change," he said.

Rutte said NATO was "in close contact" with its partners, particularly South Korea, which was taking part in this week's talks as part of the so-called Indo-Pacific four, along with Australia, Japan and New Zealand.

"We will certainly have that conversation with them to get all the evidence on the table," said the NATO chief.

Seoul's spy agency said Friday that North Korea had decided to send "large-scale" troops to support Moscow's war in Ukraine, with 1,500 special forces already in Russia's Far East and undergoing training.

The South Korean National Intelligence Service released detailed satellite images it said showed a first deployment, saying it estimated the North could send around 12,000 soldiers in total.

Pyongyang and Moscow have been allies since North Korea's founding after World War II. They have drawn even closer since Russia's 2022 invasion of Ukraine, with Seoul and Washington long claiming that Kim Jong Un has been sending weapons for use in Ukraine.

"Even if North Korea is not physically there at the battlefield then still, they are helping to fuel Russia's war of aggression against Ukraine in every way they can," Rutte said.