U.S. President Joe Biden announced Wednesday the United States is bolstering its military presence in Europe, including the deployment of additional naval destroyers in Spain and positioning more troops elsewhere.

Biden, in Madrid for a 30-nation NATO summit, said the U.S. would establish a permanent headquarters for the U.S. 5th Army Corps in Poland, add a rotational brigade of 3,000 troops and 2,000 other personnel to be headquartered in Romania, as well as send two additional F-35 fighter jets to Britain.

'Today, I'm announcing the United States will enhance our force posture in Europe to respond to the changed security environment, as well as strengthening our collective security," Biden said.

NATO leaders are gathering for a summit that will include discussion of support for Ukraine and how the West's military alliance - formed after World War II - will adapt to face current and future challenges.

'Earlier this year, we surged 20,000 additional U.S. forces to Europe to bolster our lines in response to Russia's aggressive move, bringing our force total in Europe to 100,000. We're going [to] continue to adjust our posture based on the threat in close consultation with our allies,' Biden said.

The leaders are expected to agree at the summit to boost support for Ukraine as it defends itself from a Russian invasion. Ukrainian President Volodymyr Zelenskyy is addressing the summit by video.

Biden said that at a time when Russian President Vladimir Putin 'has shattered peace in Europe and attacked the very tenets of rule-based order,' the United States and its allies are 'proving that NATO is more needed now than it ever has been, and it's as important as it ever has been.'

NATO Secretary General Jens Stoltenberg told reporters the gathering will be a 'historic and transformative summit for our alliance,' adding that it comes amid 'the most serious security crisis we have faced since the Second World War.'

Workers paste posters announcing the NATO Summit outside the Madrid Fair in Madrid, June 27, 2022.

Russia's attack is also influencing NATO's own long-term plans, with a new strategic concept that includes what the alliance has called its 'changed security environment.'

National Security Council spokesman John Kirby told reporters the strategic concept, which was last updated in 2010, will mention China for the first time, 'and quite frankly the deepening strategic partnership that we see evolving between Russia and China and how that affects our allies.'

'I won't get ahead of the exact language, but clearly our allies have likewise been concerned about this growing, burgeoning relationship between Russia and China,' Kirby said. 'They have had growing concerns about China's unfair trade practices, use of forced labor, theft of intellectual property and their bullying and coercive activities, not just in the Indo-Pacific, but around the world.'

In the short term, NATO is strengthening its readiness to respond to outside threats, including boosting the number of troops under direct NATO command and pre-positioning more heavy weapons and logistical resources.

Celeste Wallander, U.S. assistant secretary of Defense for International Security Affairs, told reporters the new U.S. deployments to Europe are significant 'precisely because of the changed security environment and the recognition that the United States needs to have a longer-term capability to sustain our presence, our training, our activities and our support to the countries of the eastern flank, both bilaterally and through the NATO battle groups.'

As NATO invites Sweden and Finland to join the alliance, the summit also is set to include talks about reinforcing partnerships with non-NATO countries. Participating in the summit are leaders from Australia, Japan, South Korea and New Zealand.

'President Putin has not succeeded in closing NATO's door,' Stoltenberg said. 'He's getting the opposite of what he wants. He wants less NATO. President Putin is getting more NATO by Sweden and Finland joining our alliance.'

Other areas of discussion include terrorism, cyberattacks and climate change.

VOA's Chris Hannas contributed to this story.