Updated

The pivotal Nordic countries of Finland and Sweden formally applied to join the North Atlantic Treaty Organization Wednesday, amid Russia's continuing invasion of Ukraine.

NATO Secretary-General Jens Stoltenberg told reporters that the treaty organization had formally accepted the applications, which have been in development over the past week.

"I warmly welcome the requests by Finland and Sweden to join NATO. You are our closest partners," Stoltenberg told reporters after a receiving their application letters from the two Nordic countries’ ambassadors.

"It’s an absolute certainty that NATO will approve Finland and Sweden’s application for membership… This will fundamentally transform the balance of power between Russia and the West, in Northern Europe, in favor of the alliance," said Rebekah Koffler, a former Defense Intelligence Agency intelligence officer and the author of  "Putin’s Playbook: Russia’s Secret Plan to Defeat America." She added, "Russia’s nuclear-capable Iskander missile presents a serious threat to NATO forces, however."

KREMLIN CALLS FINLAND'S NATO MOVE A THREAT TO RUSSIA

NATO's 30 member countries will now weigh the applications. The process is expected to take about two weeks, although Turkish President Recep Tayyip Erdogan has expressed reservations about the Nordic countries joining.

The Turkish leader explained his opposition by citing Sweden and other Scandinavian countries’ alleged support for Kurdish militants and others whom Turkey considers to be terrorists

"We are following developments concerning Sweden and Finland, but we are not of a favorable opinion," Erdogan said in Istanbul.  

Finland's President Sauli Niinisto

Finland's President Sauli Niinisto makes a point during a joint press conference with British Prime Minister Boris Johnson, at the Presidential Palace in Helsinki, Wednesday, May 11, 2022. (AP Photo/Frank Augstein, Pool, File)

If Finland and Sweden overcome Erdogan's objections, they could become members in a few months. While the process usually takes eight to 12 months, NATO wants to move quickly given the threat of Russia.

The Kremlin has warned that Finland and Sweden joining NATO would represent a threat to Russia, and has threatened to deploy nuclear warheads to the border with Finland should the alliance go through.

In an abrupt about-face, however, Russia's Foreign Minister Sergei Lavrov later said that the Russian neighbors joining NATO "makes no big difference."

Russian Foreign Minister Sergey Lavrov

Russian Foreign Minister Sergey Lavrov pauses during a news conference in Moscow, Nov. 30, 2021. (Russian Foreign Ministry Press Service via AP)

Germany and the United States already have agreements to defend Finland and Sweden against Russian aggression.

Sweden NATO application

Sweden's Minister of Foreígn Affairs Ann Linde signs Sweden's application for NATO membership in Stockholm, Sweden, on May 17, 2022. (Henrik Montgomery/TT News Agency/AFP via Getty Images)

Sweden has avoided military alliances for more than 200 years, while Finland adopted neutrality after being defeated by the Soviet Union in World War II. Finland has an 810-mile border with Russia.

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The capital city of Finland, Helsinki, sits across the Gulf of Finland from Russia's historic capital, St. Petersburg. 

Finland NATO application

Finnish Foreign Minister Pekka Haavisto signs a petition for NATO membership in Helsinki on May 17, 2022. (Antti Aimo-Koivisto/Lehtikuva/AFP via Getty Images)