US President Joe Biden has voiced emphatic support for bids by Sweden and Finland to join NATO amid the war in Ukraine as he hosted the two Nordic countries’ leaders in Washington, DC.

Flanked by Swedish Prime Minister Magdalena Andersson and Finnish President Sauli Niinisto, Biden told reporters on Thursday that Stockholm and Helsinki have the “total, complete backing” of Washington in their application for NATO membership.

“They meet every NATO requirement and then some,” the US president said. “Having two new NATO members in the high north will enhance the security of our alliances and deepen our security cooperation across the board.”

Sweden and Finland officially submitted applications to join NATO on Wednesday.

Although previously neutral, Swedish and Finnish leaders have cited fears of possible Russian aggression after Russia invaded Ukraine as the driving factor behind their push to join the US-led bloc.

NATO countries have a collective defence pact – article 5 of the treaty spells out that an attack on one member is considered an attack on all.

Biden announced that he is submitting reports on NATO accession for the two countries to the Senate, so lawmakers can approve the move “efficiently and quickly”.

Because NATO operates under a formal treaty, the US Senate needs to approve new members by two-thirds of the votes in the 100-member legislative chamber. But with bipartisan support for expanding the alliance, the European countries’ application is not expected to be held back in Congress.

Where their bids are facing trouble, however, is the required unanimous approval of all 30 NATO members. Turkey has voiced opposition to admitting the two nations into the alliance.

Turkish President Recep Tayyip Erdogan reiterated on Thursday that his government “will say no” to Sweden and Finland’s NATO bids. “We will keep following this path,” he said.

Turkey has accused the European countries of harbouring “terrorists”, referring to the Kurdistan Workers’ Party (PKK) and the Gulen movement, which Ankara has said was behind the 2016 failed coup against Erdogan’s government.

On Thursday, Finland’s Niinisto said as a NATO member, his country would commit to Turkey’s security.

“We take terrorism seriously,” Niinisto said. “We condemn terrorism in all its forms and we are actively engaged in combating it. We are open to discussing all the concerns Turkey may have concerning our membership in an open and constructive manner.”

US Secretary of State Antony Blinken had met his Turkish counterpart Mevlut Cavusoglu at the United Nations on Wednesday, with both countries committing to strengthen bilateral ties. That same day, Biden said, “We’re going to be OK,” when asked about Turkish objections to the NATO expansion efforts.

At the White House on Thursday, all three leaders stressed that NATO is a defensive alliance that does not pose a threat to other nations, implicitly addressing Russian concerns about the alliance’s growing reach.

Andersson, the Swedish prime minister, said the invasion of Ukraine pushed her country to reassess its historical policy of non-alignment.

“Russia full-scale aggression against a sovereign and democratic neighbour, that was a watershed moment for Sweden,” she said. “And my government has come to the conclusion that the security of the Swedish people will be best protected within the NATO alliance.”