Russia has launched a new wave of alleged attacks targeting arms manufacturers in Europe, including Bulgaria, as part of a campaign that Western intelligence believes is designed to test NATO's response without triggering the alliance's collective-defense clause, The Daily Telegraph reported, citing Western intelligence sources.

According to the report, the Kremlin is recruiting members of local criminal groups to carry out acts of sabotage against defense companies. Intelligence officials believe the operations are being carefully planned to remain below the threshold that could lead to the activation of Article 5, which treats an armed attack against one NATO member as an attack against all.

The latest case emerged in Estonia, where Latvia this week detained three of its citizens suspected of setting fire to a drone manufacturing facility in neighboring Estonia. The building, owned by Tallinn-based Milrem Robotics, was set ablaze on the night of August 15.

Milrem Robotics supplies weapons to Ukraine and is one of two foreign companies providing unmanned ground vehicles to the Ukrainian armed forces. Estonian Prime Minister Kristen Michal said following the incident that investigators were examining whether the fire was an act of sabotage and whether Russia could have been involved.