Estonia has formally blamed Russian security services for an arson attack on a defence company in Tallinn that supplies unmanned military vehicles to Ukraine.

The fire broke out overnight on August 15 at a building used by Milrem Robotics. Estonia’s Internal Security Service, known as KAPO, concluded it was a deliberate, pre-planned act commissioned by Russia. Three Latvian suspects were detained in Latvia on August 17 and 18 and handed over to Estonia.

Milrem makes THeMIS unmanned ground vehicles, with 15 units operating in Ukraine and more than 150 more expected under a programme funded by the Netherlands. The company said the fire had no material impact on operations.

Foreign minister Margus Tsahkna called the act absolutely unacceptable and summoned Russia’s charge d’affaires. Prime minister Kristen Michal said Estonia would respond with stronger security, more support for Ukraine and greater pressure on Russia.

Kremlin spokesman Dmitry Peskov rejected the claims as unfounded. NATO secretary general Mark Rutte backed Estonia, saying alleged sabotage would not cut allied support for Ukraine.