The Nordic nation, which shares a border with Russia, applied to join the military alliance in the wake of Vladimir Putin's invasion of Ukraine last year.

It is the first enlargement of NATO since North Macedonia joined the alliance in 2020.

The announcement was confirmed by NATO secretary general, Jens Stoltenberg, who said the move will make Finland and other members safer.

"We will raise the Finnish flag for the first time here at NATO headquarters. It will be a good day for Finland's security, for Nordic security and for NATO as a whole," he told reporters in Brussels.

He also expressed his hope that Finland's neighbour Sweden will be permitted to join in the coming months.

Russia immediately responded to the announcement, with an official telling state-owned news agency RIA that the country would bolster forces along its 1,300km (810 mile) border with Finland.

'We will strengthen our military potential in the western and northwestern direction," Russia's deputy foreign minister Alexander Grushko told RIA.

"In the event that the forces and resources of other NATO members are deployed in Finland, we will take additional steps to reliably ensure Russia's military security."

Finnish president Sauli Niinistö, defence minister Antti Kaikkonen and foreign minister, Pekka Haavisto, are now due to attend a ceremony to mark Finland's membership of NATO.

"It is a historic moment for us. For Finland, the most important objective at the meeting will be to emphasize NATO's support to Ukraine as Russia continues its illegal aggression," Mr Haavisto said in a statement.

"We seek to promote stability and security throughout the Euro-Atlantic region."

Turkey was the last of NATO's 30 members to accept Finland's application - which ends the country's decades of military non-alignment.

Turkey's president Recep Tayyip Erdogan said earlier in March that Finland had secured his country's blessing after taking concrete steps to keep promises to crack down on groups seen by Ankara as terrorists, and to free up defence exports.

However, Turkey is still blocking the approval of Sweden joining NATO, with the government saying Stockholm has so far failed to sufficiently crackdown on similar groups.

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Turkey has repeatedly said Sweden needed to take additional steps against supporters of Kurdish militants and members of the network it holds responsible for a 2016 coup attempt.

Ankara treats both groups as terrorist organisations.

Talks between Sweden and Turkey have made little progress, especially following several disputes mainly over street protests by pro-Kurdish groups in Stockholm.

Mr Stoltenberg urged Turkey to ratify Sweden's application. A vote on Sweden's bid has also not yet been scheduled in Hungary,

Officials in Budapest last month revealed that grievances over criticism by Stockholm of Prime Minister Viktor Orban's policies was behind its objection.

NATO must agree unanimously for new members to join.