Nato leaders discussed plans to overhaul and boost the alliance’s defences at the alliance's Madrid summit, including establishing a new force model that would place about 300,000 troops on high alert to deal with any future threats.
As well as the Polish base for the Fifth Army Corps, Mr Biden said his country would also maintain an additional rotational brigade of thousands of troops in Romania and bolster deployments in the Baltic states. The US will send two more F-35 squadrons to the UK and add to air-defence systems in Germany and Italy. That adds to 100,000 American troops already in Europe.
“In a moment where Putin has shattered peace in Europe and attacked the very, very tenets of the rule-based order of the United States and our allies — we’re stepping up,” Mr Biden said at the summit. “The steps we’re taking during this summit are going to further augment our collective strength.” The Russian president is “getting the NATO-ization of Europe," he added.
Nato will be "strengthened in all directions across every domain - land, air and sea," he said. Biden visited Poland in March and told US troops deployed there that they were "in the midst of a fight between democracies and oligarchs."
Poland, which has long sought a permanent US military base on its soil, on Wednesday said the move would send a clear signal to the Russians.
"It is a success which comes from long and consistent negotiations on this matter and, at the same time, a very clear sign that the Americans intend to increase, not decrease, their presence in Poland," said Jakub Kumoch, the Polish president's foreign policy adviser.
"Something that seemed impossible to many is becoming a fact today," Deputy Foreign Minister Marcin Przydacz wrote on Twitter. "We have a PERMANENT U.S. presence in Poland ... It is also a clear signal to Moscow."
Russian forces struck targets in the Mykolaiv region of southern Ukraine on Wednesday and intensified attacks on fronts across the country.
Ukrainian President Volodymyr Zelenskyy told the Nato leaders his country needed more weapons and money to defend itself against Russia, warning that Moscow's ambitions did not stop at Ukraine.
In a video link-up from the capital Kyiv, demanded more weapons from the West and said Ukraine needed $5 billion per month for its defence and protection.
Russia would set its sights on other countries, he warned, saying Moscow wanted to "enslave" NATO-member Lithuania.
"This not a war being waged by Russia against only Ukraine. This is a war for the right to dictate conditions in Europe - for what the future world order will be like," he said.
Russia said Wednesday it would not be intimidated by US military reinforcements in Europe as tensions spiral over Moscow's military intervention in Ukraine.
"I think that those who propose such solutions are under the illusion that they will be able to intimidate Russia, somehow restrain it - they will not succeed," Deputy Foreign Minister Sergei Ryabkov said.
"The security of countries where additional contingents will appear will not be strengthened. The prospect of stabilisation will be distant. Risks will increase," he added.
He said Russia would respond.
Arriving at the summit in Madrid, UK Prime Minister Boris Johnson said Mr Putin was getting "more Nato", not less, as a result of his actions in Ukraine.
On Tuesday, Nato Secretary General Jens Stoltenberg said countries need to significantly increase their defence spending in a “more dangerous and unpredictable world”, where Ukraine is paying the price for freedom.
The alliance had already on Tuesday night moved one step closer to bolstering its eastern front with Russia after Turkey dropped its opposition to Swedish and Finnish bids to join. Once members, the Nordic countries will augment the alliance with their Nato-standard militaries and high level of integration. Both countries are also boosting defence spending.
President Recep Tayyip Erdogan emerged from the meeting declaring victory after securing a 10-point agreement under which the two countries vowed to join Turkey's fight against banned Kurdish militants and to swiftly extradite suspects.
Turkey put the deal to the immediate test by announcing that it would seek the extradition of 12 suspects from Finland and 21 from Sweden.
Nato hopes adding them will shrink the vulnerability of other countries in the Baltic region with the option to quickly reinforce from the north in the event of an attack. The additional 1,343 kilometres of land frontier with Russia would effectively isolate its enclave of Kaliningrad sandwiched between Poland and Lithuania on the Baltic Sea.
Mr Stoltenberg on Wednesday said the alliance would invite the two Nordic countries to join while leaders are still in Madrid.
He called the invitation “a historic decision”, with the alliance’s 30 members then due to ratify membership. “I expect that also to go rather quickly because allies are ready to make that ratification process happen as quickly as possible,” he said.
Turkey agreed to support inviting the two Nordic countries into the military alliance, after receiving pledges from Finland and Sweden addressing its security concerns, including restrictions on Kurdish groups that Turkey considers terrorists, and avoiding arms embargoes.
“The talks were intense and tough, not in mood but in terms of the subject matter, and after four hours, we reached an understanding,” Finnish President Sauli Niinisto said. “Turkey becoming an ally now could impact the considerations” on arms export permits on a case-by-case basis, he said.
Swedish Prime Minister Magdalena Andersson said in a phone interview: “It’s good for Sweden and Finland’s security but in equal measure it is good for Nato as we would contribute to the common security of the alliance. Sweden and Finland were able to explain our work against terrorism and how we have tightened legislation and will continue to strengthen it.”
Nato membership for the two previously neutral countries would mark a significant shift in the European security landscape after Russia’s invasion of Ukraine.
Still, the actual membership process will still take many months, including ratification from Nato members’ parliaments, before Finland and Sweden become members and can benefit from the alliance’s article 5 collective defence commitments.
Mr Stoltenberg said he expected allies to sign the Nordic countries’ accession protocols “immediately” after the summit. All 30 members need to sign off.
A senior US administration official said President Biden’s goal this week was to help propel the deal across the finish line. The US has stressed that bringing Finland and Sweden into the fold could make the alliance more secure.