Finland will become a full member of Nato on Tuesday 4 April, according to the alliance's Secretary General, Jens Stoltenberg.
"This is a historic week. Tomorrow we will welcome Finland as the 31st member of Nato, making Finland safer and our alliance stronger. We will raise the Finnish flag for the first time here at the Nato headquarters," Stoltenberg told a press conference on Monday afternoon.
Stoltenberg noted that Finland's accession was the fastest ratification process in the alliance's modern history.
"It will be a good day for Finland's security, for Nordic security, and for Nato as a whole," Stoltenberg added.
Niinistö and 2 ministers to attend ceremony
Meanwhile President Sauli Niinistö's office issued a statement confirming that Finland will become a member on Tuesday, and that he will travel to Brussels to attend the accession ceremony at Nato HQ.
It said that Finnish Foreign Minister Pekka Haavisto (Green) will deposit Finland's instrument of accession to the treaty before the foreign ministers' meeting.
Niinistö and Stoltenberg are to hold a bilateral meeting and a joint press conference before delivering remarks at the ceremony.
In addition to Niinistö and Haavisto, Defence Minister Antti Kaikkonen (Cen) will attend the flag-raising ceremony.
The announcements came after Norwegian tabloid newspaper Verdens Gang (VG) reported that preparations were underway in Brussels for the Finnish flag to be raised outside Nato headquarters on Tuesday, marking Finland's official status as a fully-fledged member of the alliance.
Citing unnamed sources, the paper reported that the last stages of Finnish membership are being feverishly finalised ahead of a two-day meeting of Nato foreign ministers in the Belgian capital, which begins on Tuesday.
In an interview with Helsingin Sanomat on Sunday evening, Haavisto said that Finland's Nato membership could be formally approved in Brussels without the need to submit documents to Washington.
Following Turkey's ratification of the Finnish application last Thursday, all 30 current member states have now accepted Finland as a member. The next, and final, stage of the accession process involves all 30 acceptance letters being received at the US State Department in Washington DC.
After that, Stoltenberg will formally invite Finland to join the organisation.
However, VG reports that the documents may instead be delivered to Brussels, where they would be handed over to US Secretary of State Antony Blinken.
"If all this goes well in the next 24 hours, the Finnish flag will be raised on the lawn outside Nato headquarters in a formal ceremony," VG writes.
The invitation letter must be signed by Haavisto, who will be attending the meeting in Brussels.
President Sauli Niinistö signed Finland's Nato bill into law on 23 March, clearing the path for Finland to formally approve the document once it is received.
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