The NATO chief said Ukraine was running a risk with the advance onto Russian territory but that it was up to Kyiv how to conduct its military campaign.

“Ukraine has a right to defend itself. And according to international law, this right does not stop at the border,” Stoltenberg told the paper, adding that NATO had not been informed about Ukraine's plans beforehand and did not play a role in them.

“President Zelenskyy has made clear that the operation aims to create a buffer zone to prevent further Russian attacks from across the border,” he said.

“Like all military operations, this comes with risks. But it is Ukraine’s decision how to defend itself.”

Kyiv launched a major cross-border incursion into the Kursk region on August 6, while Moscow’s troops keep pressing towards the strategic hub of Pokrovsk in eastern Ukraine.

The incursion was also discussed at a meeting of the NATO-Ukraine Council on Wednesday that was requested by Kyiv amid Moscow’s biggest wave of air attacks on its neighbor.

The council, grouping members of the Western military alliance and Ukraine, was established last year to enable closer coordination between the alliance and Kyiv.

Russia has labeled the Kursk operation as a “major provocation” and has said that it will retaliate.