Stoltenberg said NATO would agree to strengthen its defences at a key summit in Lithuania next week in order to protect all members, especially those which border Russia's ally Belarus.

"It's too early to make any final judgment about the consequences of the fact that Prigozhin has moved to Belarus and most likely also some of his forces will also be located to Belarus," Stoltenberg told reporters.

"What is absolutely clear is that we have sent a clear message to Moscow and to Minsk that NATO is there to protect every ally and every inch of NATO territory," he said after dinner with seven national leaders in The Hague.

"So no room for misunderstanding in Moscow or Minsk about our ability to defend allies against any potential threat, and that is regardless of what you think about the movement of the Wagner forces."

Lithuanian President Gitanas Nauseda warned of the risk of Wagner fighters being based in Belarus.

"If Wagner deploys its serial killers in Belarus, all neighbouring countries face even greater danger of instability," he told the news conference.

Mercenary boss Prigozhin arrived in Belarus on Tuesday, after a dramatic weekend revolt by Wagner fighters that posed the biggest threat of Russian President Vladimir Putin's rule.

Prigozhin, a former Kremlin ally and catering contractor, built Russia's most powerful private army and recruited thousands of prisoners to fight in Ukraine.

Stoltenberg added that the West "must not underestimate Russia" despite the chaos at the weekend.

He said it was crucial to keep supporting Ukraine against Russia's invasion and that NATO allies would thrash out a path to Kyiv's membership of the alliance.

Dutch Prime Minister Mark Rutte, who hosted the dinner, rejected Putin's claims that the West wanted Russians to kill each other.

"I refute what Putin suggested yesterday that we in the West want Russia to descend into domestic chaos -- on the contrary, instability in Russia creates instability in Europe," he said.