NATO will be "strengthened in all directions across every domain -- land, air and sea," he said at a summit of the transatlantic alliance being held in Madrid.

Biden, who was meeting with NATO Secretary General Jens Stoltenberg, said the extra forces included:

- Boosting the fleet of US naval destroyers from four to six in Rota, Spain.

- A permanent headquarters in Poland of the 5th Army Corps.

- An "additional rotational brigade" in Romania, consisting of "3,000 fighters and another 2,000 personnel combat team."

- Enhanced rotational deployments in the Baltic countries.

- Two additional squadrons of the F-35 stealth plane to Britain.

- "Additional air defence and other capabilities in Germany and in Italy."

"Together with our allies we're going to make sure that NATO is ready to meet the threats from all directions across every domain," Biden said.

"In a moment where (Russian President Vladimir) Putin has shattered peace in Europe and attacked the very, very tenets of rule-based order, the United States and our allies, we're going to step up," he said.

"We're stepping up, proving that NATO is more needed now than it ever has been and it's important as it ever has been."

Referring to NATO unity on accepting the applications of previously neutral Finland and Sweden to join the alliance, Biden said Putin's strategy in invading Ukraine had backfired.

"That's exactly what he didn't want but exactly what needs to be done to guarantee security for Europe," Biden said.

Stoltenberg commented that the expansion of NATO was "the opposite" of what Putin hoped for.