HELSINKI, Finland: Some 150 British troops have arrived in Finland to join Finnish and U.S. forces for a four-day "high-readiness exercise."

The UK's Ministry of Defense said the exercise involved 750 troops from the three nations.

It comes just weeks after the signing of an accession protocol with Finland to join NATO, beginning the process for membership after Russia's invasion of Ukraine. Sweden has also applied to join Nato.

The Kremlin has strongly opposed the two previously neutral countries joining the military alliance and has issued threats.

The British troops were in Estonia as part of the British Arm's Project Unified Stance, a series of exercises held across Europe, in coordination with Nato and its allies.

"Our soldiers, sailors and aviators have received a warm welcome in Finland over the last few months. Exercise Vigilant Fox is the latest activity in an ongoing series of events across the domains," said UK defence representative in Helsinki, Wing Commander Stephen Boyle, as quoted by the BBC.

"As Finland moves towards full Nato membership, we will continue to seek opportunities like this to show solidarity with Finland, learn from each other and improve our ability to operate together," he added.

Defence Minister James Heappey said the training "demonstrated the strength and interoperability of our armed forces with our U.S. and Finnish allies," adding that it reaffirms the UK's commitment to the defense and security of the Baltic Sea region.

Meanwhile, the UK Ministry of Defence revealed that six Royal Air Force fighter jets flew to Finland and Sweden for joint training exercises just days before the exercise.