Estonia has announced it will be closing all border crossings with Russia from the start of December after it said Russia was behind an attempted arson attack on one of its drone makers.

The country’s foreign minister, Margus Tsahkna, said there was “clear evidence that Russia’s military intelligence service, GRU, ordered a sabotage attack against an Estonian defence industry company.”

Estonian authorities detained eight suspects in connection with the attempted attack on Threod Systems’ drone manufacturing site in Viimsi, north of Tallinn, early on Saturday morning, Prosecutor General Astrid Asi told a press conference on Sunday. Threod makes long-range reconnaissance and attack drones.

The country’s internal security services posted on X: “We have quickly detained the suspects. We advise against even considering such job offers from Russia. The consequences are serious!”

The suspects are residents of neighbouring Latvia. Five have been remanded in custody.

Tsahkna said that closing all Estonia-Russian border crossing points from 1 December will “reduce Russia’s ability to conduct hostile activities in Estonia and strengthen our efforts to prevent sanctions circumvention”.

“Russia must understand that hostile actions against Estonia come with consequences. Attempts to intimidate, destabilise, or undermine our security will not go unanswered,” said Tsahkna.

Keir Giles, associate fellow of the Russia and Eurasia Programme at Chatham House, told The i Paper that closing the border was “a self-defence mechanism by Estonia as well as a demonstrative response to what Russia is doing to them”.

“For years, European countries have been looking for ways to respond to Russian sabotage and sub-threshold attacks, and eventually they have to respond,” he added.

Mark Galeotti, a historian and lecturer specialising in Russian crime and security affairs, said the border was often used by Russian Estonians visiting family members. “If the border is completely closed, that is likely to stoke dissatisfaction in that community, which might be something of an own goal … this might make them more disaffected, and thus more likely to be supportive of Moscow.”

Galeotti said Estonia had “long been about the most hawkish of EU countries”, but noted that recent sabotage attacks had not been carried out by Russians. “Saturday’s arson attack, for example, has been blamed on Latvian citizens,” he said. “This looks like Tallinn trying to look tough and seizing on an opportunity to do something it has wanted to do for some time.”

“Most EU borders with Russia are highly restricted, but only Finland has completely shut down crossing points since the end of 2023, because of a surge of migrants from the Middle East coming through Russian borders, apparently with the connivance of the authorities,” he added.

The news of the border closure came as Romania said that three commercial ships were hit by drones in the Black Sea. The Romanian prime minister, Luca Niculescu, said on Sunday that the country’s armed forces had scrambled fighter jets twice after the incident near the Sulina Canal. The canal is a shipping lane that links the Danube river to the Black Sea and is used by Ukraine for exports.

Niculescu did not identify the origin of the drones, but said they were a direct consequence of Russia’s war on Ukraine. “These incidents are unacceptable and constitute a violation of international law,” he said. “They reflect the deteriorating security situation caused by Russia’s ongoing war against Ukraine.”

Russia has denied targeting Ukraine’s neighbours with drones.

It comes ahead of a big week for diplomacy, with Donald Trump, Xi Jinping and Vladimir Putin due to hold a trilateral meeting on the sidelines of the Asia-Pacific Economic Cooperation (Apec) leaders’ meeting in Shenzhen.

Estonia’s internal security service director general, Margo Palloson, said counterintelligence had confirmed that the attempted attack was coordinated by the GRU. “This was yet another attempt by Russia to carry out an act of sabotage in Estonia,” he said.

According to Palloson, the suspects attempted to break the building’s windows and pour flammable liquids inside to set the building on fire and cause an explosion. “We assess that if this attack had succeeded in the way the attackers planned, it would have caused very significant damage to the company,” he said.

Estonia’s prime minister, Kristen Michal, said on Sunday: “This is part of Russia’s broader hybrid war against Europe, with the aim of decreasing support to Ukraine and pressure on Russia. We will not be intimidated.”

It was the second attempted arson attack on an Estonian defence company this year attributed to Russia.

In August, a fire was reported at defence contractor Milrem Robotics in Tallinn. The company supplies unmanned ground vehicles to Ukraine.