In a press release Saturday, Matthew Miller, spokesperson for the State Department, called for Serbian President Aleksander Vucic [pictured] to immediately and unconditionally release the detained officers. File photo by Andrej Cukic/EPA-EFE

“Their arrest and ongoing detention on spurious charges has exacerbated an already tense situation,” Miller said. “We also continue to call on both Serbia and Kosovo to follow the three-point plan outlined by the E.U. and return to the E.U.-facilitated dialogue without delay.”

The Kosovo police were detained on Wednesday near the Kosovo-Serbia border. Serbian officials allege that the officers were heavily armed and had explosive devices. Officials in Kosovo claim the officers were kidnapped by force.

The NATO Kosovo Force said in a statement that it is unclear where the officers were when they were detained. The agency called for de-escalation efforts from both sides, urging them to adhere to the military-technical agreement that was reached following the Kosovo War in 1999.

“We urge both parties to refrain from provocative rhetoric and to avoid any unilateral act that could escalate the tension in the area,” a statement from the NATO Kosovo Force said.

Last month, NATO and Western allies condemned Kosovo’s security forces after recent violent clashes flared. The condemnation was spurred on by unrest when officials from Kosovo attempted to forcibly enter municipal buildings amid Serbian protests.

#NATO takes the events in northern #Kosovo very seriously,” Oana Lungescu, NATO spokesperson, tweeted Sunday. “@NATO_KFOR is taking all necessary measures to ensure a safe & secure environment and freedom of movement for all communities in Kosovo, as authorised under the #UN Security Council Resolution 1244.”