Two Finnish companies are suspected of having exported drones and other military-classified products worth more than €3 million ($3.25 million) to Russia in violation of EU sanctions, Finnish Customs said.

"There are a total of six suspects, one of whom has been in custody since September," the customs agency said in a statement.

It said nearly 3,500 drones are believed to have been sent to Russia. The products also included microcontrollers, semiconductor devices and defense materials designed to stop drones.

Authorities said they suspected the items were approved for export to another nation but ended up in Russia. In the case of the anti-drone equipment, for example, the products were cleared for Kazakhstan.

Drones have been used extensively in the war in Ukraine, including for reconnaissance and to deliver explosives. 

Following Russia's full-scale invasion of Ukraine, the EU imposed 12 sets of sanctions on Russia, targeting crucial oil and gas exports, as well as technology and military products.