When the white blimp began to circle the skies near the Russian border, Estonian police weren’t quite sure what to make of it.

The strange, Zeppelin-like aircraft had been spotted on the Russian side of the frontier near Narva, a Russian-speaking Estonian town on the far edges of Nato territory.

After some debate, Estonian police chose to ignore the blimp and hoped that would be the end of the matter. But the next day, it came back – this time marked with a “Z”, the symbol of Vladimir Putin’s invasion of Ukraine.

“We are seeing things like this nearly every week,” Egert Belitšev, the director-general of the Estonian police, said during a tour of Narva’s border checkpoint, the day before Sir Keir Starmer, the Prime Minister, arrived in the country for a security summit with Baltic and Nordic leaders.

Tensions on this 200-mile frontier, which spans open fields, frozen lakes, dense forests and barren swamps, have soared in recent months according to border guards.

Police say they have seen a major increase in border security incidents, such as staged anti-West protests, attempted smuggling of weapons parts, GPS spoofing, attempts to push waves of migrants across the Estonian border and sinister aircraft stunts such as the one near Narva.

Referring to that blimp incident in June, Mr Belitšev joked that “it’s good to see that Russia is using modern technology”. But he added, rather grimly: “It was intentionally made visible to everyone, to say: ‘We are watching you.’”

The Baltic nation of Estonia, which joined Nato and the EU in 2004, still bears the scars of two Soviet occupations; today, it is one of Russia’s most vocal opponents in Europe.

In response to Russia’s invasion of Ukraine in 2022, Tallinn spent more GDP per capita on military aid for Ukraine than any other country, and it passionately supports Kyiv’s dream of joining Nato.

That support, and Estonian’s decision to impose restrictions at the Narva crossing point used by Russian speakers, has angered Putin, who in 2022 suggested he would like to see Narva returned to Moscow’s control.