The secretary general of the North Atlantic Treaty Organization has announced this week's summit in Madrid will approve the alliance's most major shift in a generation, putting 300,000 troops on high alert in reaction to the Russian invasion of Ukraine.

This would be the "largest reform of our collective defense and deterrence since the end of the cold war," Jens Stoltenberg said, prior to this week's summit of the 30-nation alliance, which runs from Tuesday to Thursday.

Stoltenberg said the military alliance's forces in the Baltic states and five other frontline nations would be expanded to "brigade levels" - between 3,000 and 5,000 soldiers.

The NATO Response Force now consists of up to 40,000 members, and the proposed adjustment amounts to a substantial revision in response to the Russian militarization.

Based on the proposals, NATO would also relocate its inventories of munitions and other supplies further east by 2023.

The Norwegian secretary general confessed he could not make any assurances regarding the status of Sweden and Finland's applications to join NATO because Turkey's objections to their membership had not been overcome.

Stoltenberg reported that Recep Tayyip Erdoan has agreed to visit Swedish Prime Minister Magdalena Andersson and Finnish President Sauli Niinisto in Madrid on Tuesday in an effort to address the matter.

However, he downplayed expectations for a breakthrough at the meeting held on the sidelines of the NATO convention.

At a press conference, he stated, "It is too early to say what type of progress you can accomplish by the summit."

Turkey has stated that it will deny the applications of Sweden and Finland until it obtains adequate guarantees that the Nordic nations are willing to address what it considers to be their backing for Kurdish terrorist groups.

After a day of meetings between representatives of the three nations in Brussels, Andersson expressed optimism that a last-minute agreement may still be struck.

Andersson emphasized that Sweden "condemns terrorism in all its forms" and that the militant Kurdish Workers' party (PKK) was designated as a terrorist organization in Sweden.

On Wednesday morning, the president of Ukraine, Volodymyr Zelenskiy, will deliver a speech at the summit, where he is anticipated to reiterate a request made on Monday at the G7 conference in Germany for western countries to contribute armaments so the battle does not "stretch on through winter."