Security around the Baltic Sea

Sources: Russian spies aboard the shadow fleet

Russian spies aboard oil tankers in the so-called shadow fleet have been spying from European waters. Ukrainian and Western intelligence sources have told CNN.

In the past six months, several of the vessels, often registered in third countries, have taken on board extra crew members shortly before sailing.

Several of these are employed by the secretive company Moran Security, which has links to the Russian military and intelligence service, according to the sources.

On at least one occasion, Moran employees are said to have photographed European military installations from oil tankers. The men are also said to be tasked with keeping an eye on the non-Russian captains on board.

– Everyone knows that these guys take orders from the Russian state, but it is difficult to prove, says Jacob Kaarsbo, a former employee of the Danish intelligence service.

Estonia: Russian border guards entered our area

Three Russian border guards entered Estonian territory on Wednesday, authorities in the country reported, according to several media outlets. The Russians crossed the Narva River in a hovercraft and patrolled along a pier for around 20 minutes. Their purpose is not known.

– They did not pose a direct security threat, but the police and border police have increased their presence, said Estonian Interior Minister Igor Taro, according to public service broadcaster ERR.

Estonia, a member of NATO, has summoned Russia's highest-ranking diplomat in connection with the incident.