Finland’s president and prime minister have called for the country to apply for Nato membership “without delay”.
Sauli Niinisto and Sanna Marin said in a joint statement they expected a decision in the next few days.
The move comes amid a surge in public support for Nato membership following Russia’s invasion of Ukraine.
Finland shares a 1,300-km (810-mile) border with Russia. Until now, it has stayed out of Nato to avoid antagonising its eastern neighbour.
Finland will formally announce its decision on Sunday after it has been considered by parliament and other senior political figures.
Sweden has said it will announce a similar decision on the same day.
Russia has threatened unspecified measures if the two governments abandon their long-standing policy of military non-alignment.
But Nato Secretary General Jens Stoltenberg has said he expects the process of giving Sweden and Finland membership to happen “quite quickly”.
President Niinisto and Prime Minister Marin said in their statement that they had wanted to give the Finnish public space to discuss the issue but that time for a decision was approaching.
“Nato membership would strengthen Finland’s security,” it said. “As a member of Nato, Finland would strengthen the entire defence alliance. Finland must apply for Nato membership without delay.”
An opinion poll last week put support in Finland for joining Nato at 76%, with 12% against, a big swing towards membership since before the invasion.
Finland and the USSR were on opposing sides in World War Two, with the Finns famously fending off a Soviet invasion in 1939-40.
But Finland lost 10% of its territory in the final peace agreement and remained non-aligned throughout the Cold War.
Its accession to Nato would more than double the length of Russia’s borders with the alliance. Sweden does not have a border with Russia.