Nato, the organisation which brings together the armies of various countries, is holding its biggest military exercise since the Cold War, rehearsing how it would respond to the invasion of an ally.

The operation, Trident Juncture, started last week and involves all 29 Nato members, as well as Finland and Sweden.

It's taking place a few hundred miles from Norway's border with Russia, amid rising tension between both sides. But Nato denies it is targeted at a specific country.