The RAF has sent four Typhoons and two F-35Bs to Finland and Sweden for joint training exercises.
It comes just weeks after Finland and Sweden applied to join NATO and is part of an “increased presence in the region”, the RAF said.
The presence was requested by the two countries.
Defence Secretary Ben Wallace said: “Finland and Sweden are important defence partners and we welcome their applications to join NATO, which will make the alliance stronger as we face a renewed threat in Europe.
“These deployments highlight our determination to enhance that partnership and ensure our forces can work together seamlessly.”
The British fighter jets have conducted “high-end warfighting training” with Finnish F-18 Hornets and Swedish Gripen aircrafts, the RAF said.
Swedish defence minister Peter Hultqvist said the joint exercises “strengthen our ability to operate together in response to a crisis in our neighbourhood”.
“This is particularly important in today’s challenging security environment.”
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The UK signed mutual security assurance declarations with Finland and Sweden in May.
They are also both members of the UK-led Joint Expeditionary Force, a coalition of 10 nations.