"Of course, Viktor Orban is not representing NATO at these meetings. He's representing his own country," Stoltenberg said.

"Hungary agrees that Russia is responsible for the war. Russia is the perpetrator, and Russia can end this war today by stopping attacking Ukraine," he added.

Orban unsettled EU and NATO allies by flying to Moscow on Friday to sit down for talks with Putin, with whom he has long fostered friendly relations.

Putin said he viewed Orban as a representative for Europe -- despite EU leaders emphasising that Orban was acting on his own initiative in an exclusively bilateral role with no mandate to speak for the bloc.

Stoltenberg said he expected Orban would have "opportunities to discuss" what came up in his conversation with Putin in a NATO summit taking place in Washington next week.

While NATO is not directly involved in helping Ukraine defend itself from Russia's full-on invasion, most of its member countries are supplying military, financial and political support to Kyiv.

Hungary has not given military aid but has ended up going along with its allies' initiatives, even if reluctantly and at times after weeks of obstruction.