All NATO allies agree that "Ukraine will become a member of the alliance," its chief Secretary General Jens Stoltenberg said on Thursday.

“All allies agree that the NATO’s door is open for new members,” Stoltenberg told reporters ahead of an informal meeting of NATO foreign ministers in Oslo. “It's not for Moscow to have a veto against the NATO enlargement.”

Part of Russia’s premise for its invasion of Ukraine was to fend off NATO from expanding close to its borders.

Even though Ukraine is not a member of the alliance, and NATO has insisted that it is not a party to the conflict, the bloc has played a critical role in supporting Kyiv, donating billions in military aid and other support.

On Thursday, Stoltenberg said NATO's most important task was to ensure that Ukraine prevails in the war against Russia — and to prevent the conflict from spilling over beyond Ukraine's borders.  “That's the reason why we have increased our major presence in Eastern lines on NATO territory,” he said.

New faces at NATO: Finland’s accession to the alliance earlier this month marked a major shift in the security landscape in northeastern Europe, more than doubling NATO’s frontier with Russia.

Finnish public support for accession snowballed following the invasion of Ukraine, and also reignited calls from Kyiv to join.

Sweden also applied to join the bloc shortly after Russia's full-scale invasion began, with the support of an overwhelming majority of NATO members — but its membership has so far been held up by Turkey and Hungary.

Turkey has accused Sweden of harboring members of terrorist groups, which Stockholm denies, while Hungary has claimed Sweden behaved hostilely toward its government.

Stoltenberg said Thursday he would soon travel to the Turkish capital of Ankara to discuss Sweden's NATO membership, though did not specify the timing.

"My message is that Swedish membership, full-fledged membership of NATO, is good for Sweden, it is good for the Nordic countries, it is good for Norway, for the Baltic region, but it is also good for the whole of NATO," he said.