However, Finland’s arrival remains a bittersweet moment for the alliance as it is hoped that Sweden will join at the same time.
Helsinki’s first act as a new member was to support Stockholm’s bid.
Budapest and Ankara remain nonparticipants after belatedly agreeing to accept Helsinki’s bid.
Sweden has upset Hungarian leader Viktor Orban – one of Putin’s closest allies in Europe – by voicing alarm over the rule of law in Hungary.
It has also angered Türkiye by refusing to extradite dozens of suspects President Recep Tayyip Erdogan has linked to the failed 2016 coup plot and the Kurds’ decades-long struggle for independence.
The United States and other NATO members led the call for Sweden to join just as the Finnish flag fluttered in the cold breeze in Brussels.
“Sweden is also a strong and capable partner, ready to join NATO,” said US Secretary of State Antony Blinken.
“We encourage Túrkiye and Hungary to ratify the accession protocols for Sweden immediately.”
Ukraine is also pushing for eventual NATO membership, but Western diplomats say that remains a distant prospect.
“There is no better strategic solution to ensure strategic security in the Euro-Atlantic region than Ukraine’s membership in the alliance,” Ukrainian Foreign Minister Dmytro Kuleba said.
Stoltenberg said Ukrainian President Volodymyr Zelenskyy had been invited to NATO’s Vilnius summit in July.
The alliance’s focus remains on bolstering Kyiv’s ability to win the war, while at the same time making it a NATO member for longer.