U.S. President Joe Biden expressed strong support for the applications of Sweden and Finland to join NATO as he met with the leaders of the two countries at the White House, calling them two “great democracies” and “highly capable partners.”

Biden said he was proud to welcome Swedish Prime Minister Magdalena Andersson and Finnish President Sauli Niinisto on May 19 to mark the “momentous” applications of the formerly neutral countries. He offered “the strong support of the United States” for their applications “to join the strongest most powerful defensive alliance in the history of the world.”

Biden added that his administration on May 19 would submit reports on the two countries’ NATO accession to the U.S. Congress, which must approve the expansion of the alliance.

“They meet every NATO requirement and then some,” he said, and “having two new NATO members in the high north will enhance the security of our alliance.”

Prior to formally submitting their bids on May 18, Sweden and Finland said the war in Ukraine prompted the move to reverse their long-standing neutrality and apply for membership in NATO, whose expansion was cited by Russian President Vladimir Putin as a justification for Russia’s invasion.

“New members joining NATO is not a threat to any nation,” Biden said in a reference to Putin’s demand that the alliance stop expanding. “It never has been.”

Andersson and Niinistro later visited the U.S. Capitol and met with House Speaker Nancy Pelosi (Democrat-California), who said she was honored to offer “the fullest support and endorsement” of their request to be part of NATO.

While the processing of the two countries’ applications is expected to move quickly, it still must overcome an obstacle in Turkey’s opposition.

Niinisto said Finland was open to discussing Turkey’s concerns, adding that the country is ready to commit to Ankara’s security.

Turkish President Recep Tayyip Erdogan has said he is against their accession because of what he called their support for “terrorist organizations,” a reference to the banned Kurdistan Workers Party (PKK) and the Kurdish militia People’s Defense Units (YPG) in Syria.

On May 19, Erdogan reiterated his opposition, saying Turkey was “determined” to block Sweden’s and Finland’s bids to join NATO, calling Sweden in particular a “complete terror haven.”

The Finnish and Swedish leaders said their governments already are in discussion with Erdogan to try and overcome Turkey’s opposition.

“As NATO allies, we will commit to Turkey’s security, just as Turkey will commit to our security,” Niinisto said. “We take terrorism seriously. We condemn terrorism in all its forms and we are actively engaged in combating it.”

Washington also believes Turkey’s concerns can be overcome.

“We’re confident that at the end of the day Finland and Sweden” will enter NATO and “that Turkey’s concerns can be addressed,” U.S. national-security adviser Jake Sullivan said on May 18.

The two Nordic countries’ choice to join NATO marks a watershed in the current European security architecture.

Helsinki chose to remain neutral in the postwar era following two wars with the Soviet Union that saw Finland lose one-tenth of its territory, while Sweden has been traditionally nonaligned for the past two centuries.

Both Sweden and Finland are members of the European Union, and the latter shares a 1,340-kilometer-long of border with Russia.