Turkish President Recep Tayyip Erdogan accused Sweden and Finland of supporting terrorism on Saturday, indicating that Ankara likely won't let up its opposition to the Scandinavian countries joining the North Atlantic Treaty Organization amid Russia's invasion of Ukraine. 

"For as long as Tayyip Erdogan is the head of the Republic of Turkey, we definitely cannot say 'yes' to countries which support terrorism entering NATO," Erdogan told reporters as he returned from Azerbaijan on Saturday. 

Sweden and Finland formally applied to join NATO earlier this month, which would represent a historic expansion of the Western military alliance. 

Turkish President Erdogan

Turkey's President Recep Tayyip Erdogan speaks as he participates in a video conference with European Commission President Ursula von der Leyen and European Council President Charles Michel, from an old Ottoman palace, in Istanbul, Friday, March 19, 2021.  ((Turkish Presidency via AP, Pool))

While NATO Secretary-General Jens Stoltenberg has said that the two Nordic countries are welcome, but all 30 member nations must unanimously approve a country's application to join the alliance. 

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Turkey's opposition to Sweden and Finland's entry into NATO stems from the Scandinavian countries' alleged support for members of the Kurdistan Workers Party militant group (PKK), which Turkey and the U.S. consider a terrorist group

The PKK, which wants to establish an ethnic homeland for the Kurds, has been at war with Turkey since 1984. 

Biden in Brussels

President Joe Biden speaks during a media conference, after a NATO summit and Group of Seven meeting, at NATO headquarters in Brussels (AP Photo/Markus Schreiber)

Sweden and Finland also halted arms sales to Turkey in 2019 after the country launched an incursion into northern Syria. 

U.S. Secretary of State Antony Blinken said Friday that he is confident Turkey will be able to work out its differences with Sweden and Finland. 

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"The United States fully supports Finland and Sweden joining the Alliance, and I continue to be confident that both countries will soon be NATO Allies," Blinken said at a press conference alongside Finnish Foreign Minister Pekka Haavisto. 

"Finland and Sweden are speaking directly to and with Turkey, and working through some of the concerns that Turkey has raised and finding ways to address them."

The process for joining NATO usually takes eight months to a year, but the alliance has indicated it wants to expedite the approval amid Putin's invasion of Ukraine. 

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Kremlin spokesperson Dmitry Peskov said that Russia views Finland's entry into NATO as a "threat," though Russian Foreign Minister Sergei Lavrov later downplayed the move as making "no big difference."

Reuters contributed to this report.