Denmark has accused a Russian warship of firing two emergency flares at one of its helicopters while it was tracking the vessel in the Baltic Sea.

The Danish government has summoned the Russian ambassador over the incident, which it said happened during a “routine” monitoring operation on Monday.

Prime Minister Mette Frederiksen branded the Russian action “reckless” and said it was designed to “intimidate and divide”.

Russia said it would “thoroughly investigate” the incident but accused Danish helicopters of making “dangerous manoeuvres” near Russian warships.

It came on the same day that Nato forces shot down a drone over Lithuania in the latest security scare on the alliance’s eastern flank, where tensions remain high amid Russia’s full-scale invasion of Ukraine.

In a statement detailing the incident in the Baltic Sea, the Danish armed forces said: “One of the air force’s Fennec helicopters was today fired at with flares during a routine photographic operation of a Russian frigate, which was located in international waters off Gedser.”

Of the two flares fired at the helicopter, one passed close to it, the statement added.

The Danish foreign ministry described the incident as “completely unacceptable”.

Danish Foreign Minister Lars Lokke Rasmussen accused Russia of “gradually shifting the boundary for what they consider acceptable behaviour”, adding: “That is something we cannot accept.”

In a statement, Russian ambassador Vladimir Barbin said Moscow would “thoroughly investigate all the circumstances of the incident” but accused the Danish helicopter of carrying out “provocative actions”.

Barbin said this was “not the first time that Danish Air Force helicopters have carried out dangerous manoeuvres near Russian warships”.

He said he had complained about a similar incident last year, adding that the latest event showed that “communication problems lie not with the Russian Navy’s vessels, but with the Danish side”.

Russia’s behaviour was “reckless and dangerous,” the President of the European Commission Ursula von der Leyen said in a post on social media.

This incident – together with the drone over Lithuania – was “part of a broader pattern of Russian aggression and provocation against Europe”, she added.

Danish Defence Minister Jeppe Bruus told Reuters no attempt to make contact with helicopters had been made by the frigate’s crew.