Finland's national flag and NATO flag outside the headquarters of the Finnish Foreign Ministry in Helsinki on April 4, 2023 (Photo: Reuters)

A flag raising ceremony marking Finland's NATO admission was held at NATO headquarters in Brussels, attended by senior NATO and Finnish leaders and US Secretary of State Antony Blinken.

After NATO Secretary General Jens Stoltenberg handed over a letter inviting Finland to join the alliance, Finnish Foreign Minister Pekka Haavisto gave Finland's accession documents to Antony Blinken, US Secretary of State. The US is entrusted by NATO with storing legal documents concerning alliance membership.

Addressing the ceremony, officials said this historic event marks an important step for NATO in expanding its influence and maintaining security in the Euro-Atlantic region.

Stoltenberg said the Finnish military is highly capable and the Finnish and NATO militaries have been close partners for many years.

Finland, the 7th NATO country in the Baltic Sea, will give NATO an additional 1,340 km of shared border with Russia.

On Tuesday, Russian Defense Minister Sergei Shoigu said Finland's accession increases the risk of the Ukraine conflict escalating, because Russia considers NATO expansion a threat to its security.