Finnish President Sauli Niinistö will travel to Brussels on Tuesday, April 4 to attend an accession ceremony at NATO headquarters, officially marking the start of the country's membership of the military alliance.

Finland submitted a joint application for NATO membership alongside Sweden shortly after Russia invaded Ukraine in February 2022.

While Finland's membership has been ratified by all member states, Sweden's bid has been stalled due to opposition from Hungary and Turkey.

Finland, which shares a land border with Russia, will now become the 32nd member of the transatlantic military alliance.

"Finland will deposit its instrument of accession to the North Atlantic Treaty with the US State Department in Brussels on Tuesday, 4 April, before the start of the meeting of NATO Ministers of Foreign Affairs. The deposit will be made by Minister for Foreign Affairs Pekka Haavisto," the presidency said in a statement Monday.

A flag-raising ceremony marking Finland's accession to NATO will follow.

Niinistö and NATO Secretary General Jens Stoltenberg will hold a bilateral meeting followed by a press conference and both are expected to deliver remarks at the ceremony.

“This is a historic week,” Stoltenberg told reporters on the eve of a meeting of Nato foreign ministers in Brussels.

“From tomorrow, Finland will be a full member of the alliance.” He said he hoped Sweden would be able to join in coming months.Stoltenberg, a former Norwegian prime minister, said that on Tuesday afternoon, “we will raise the Finnish flag for the first time here at the Nato headquarters. It will be a good day for Finland’s security, for Nordic security, and for Nato as a whole.”

Stoltenberg said Turkey, the last country to ratify Finland’s membership, would hand its official texts to the US secretary of state, Antony Blinken, on Tuesday. Stoltenberg said he would then invite Finland to do the same.

The Finnish president, Sauli Niinistö, and the defence minister, Antti Kaikkonen, will attend the ceremony, along with the foreign minister, Pekka Haavisto.

“It is a historic moment for us. For Finland, the most important objective at the meeting will be to emphasise Nato support to Ukraine as Russia continues its illegal aggression,” Haavisto said in a statement. “We seek to promote stability and security throughout the Euro-Atlantic region.”