The NATO-led peacekeeping mission in Kosovo has said it is taking “very seriously” reports that its troops were spied on, following the arrest of a Croatian military officer and a Serbian woman on espionage charges.

The Split County Court in Croatia confirmed on Wednesday that the pair had been placed in pre-trial detention as part of an ongoing investigation. While details remain limited, local media reported that the officer a Croatian army pilot deployed with KFOR and his girlfriend are suspected of leaking sensitive information on troop movements in Kosovo to a Serbian group over the past three years.

“We take these allegations very seriously. The safety of KFOR personnel and the integrity of classified information are paramount,” a NATO official told AFP.

The Croatian state news agency HINA reported that the investigation involves both civil and military police, as well as Europol. According to media reports, the officer allegedly passed on details of NATO troop deployments in northern Kosovo to his partner, who is suspected of relaying the information to Serb List, a Belgrade-backed political party representing Kosovo’s Serb minority.

Kosovo government spokesman Perparim Kryeziu said Pristina was ready to fully cooperate with Croatian authorities, stressing the importance of clarifying the network behind the suspected espionage.

The Croatian President, Zoran Milanovic, has also expressed support for the probe.

KFOR troops have remained in Kosovo since the end of the 1998–1999 conflict between ethnic Albanian guerillas and Serbian forces. Kosovo declared independence in 2008, a move Serbia has not recognised, and tensions continue to flare in the Serb-dominated northern municipalities.

NATO said its forces would continue to uphold their UN mandate to ensure a safe and secure environment for all communities in Kosovo despite the latest allegations.