Speaking at a peace conference in Montreal, Foreign Minister Andrii Sybiha said the North Korean troop deployment marked a "true escalation of this war" and that Kyiv should be allowed to use missiles to strike Russian territory.

"We need a strong reaction," he said. "We need (a) strong decision of our allies to lift all the restrictions, to lift all the restrictions to use long-range missiles on the territory of Russia."

"That's our right of self defense and we are speaking about military targets on Russian territory," he added.

Citing US intelligence, Secretary of State Antony Blinken said that some 8,000 of the 10,000 North Korean troops believed to be in Russia have made their way to the Kursk border region.

North Korea has denied sending troops to Russia, but in state media last week, its vice foreign minister said that if such a deployment were to happen, it would be in line with international law.

In Montreal, Sybiha was backed by Norwegian Foreign Minister Espen Eide who said: "I just wanted to add my voice to those saying that we should not put any other restrictions on Ukraine's use of weapons."

"They want to use these weapons against military targets, military targets that are relevant for Russia in their attacks on Ukraine. And that should be the only restriction," he said, adding that Canada and a number of European countries also supported this view.