"The Turks have hoped that I will be there to receive the answer when they announce the decision. Of course, I accepted the invitation and will go to receive his expression of intent," Finnish President Sauli Niinisto said.

Erdogan hinted at giving Finland the green light earlier on Wednesday and said that "we will do our part, we will keep the promise we gave."

"On Friday we will meet with Mr President, we will do what our promise requires," he told reporters.

The ratification will formally need to pass through a vote in Turkey's parliament.

Finland, Sweden and Turkey penned a three-way deal at a NATO summit in Madrid in June, and Turkey has expressed repeated frustrations with what it views as Sweden's failure to follow through on commitments, while noting it is comfortable with Finland's progress.

Swedish Prime Minister Ulf Kristersson said Tuesday that the likelihood of Finland joining NATO before Sweden had "increased" in recent weeks, but stressed entry was just a matter of time.

"I will continue my work to support Swedish membership of NATO," Niinisto said, adding he had discussed the matter with Kristersson.

Finland and Sweden dropped decades-long policies of military non-alignment and applied to join the western alliance last May in the wake of Moscow's invasion of Ukraine.

Ankara suspended negotiations with Sweden after protests in January that included a Koran burning outside Turkey's embassy in Stockholm, but talks resumed in Brussels on March 9.