"One UNMIK staff member, a Russian national, has been released," it said.
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Earlier in the day, Mikhail Krasnoshchekov, Russian employee of the UN Mission in Kosovo, was detained by Kosovar police in the north of the self-proclaimed republic.
Kosovar police conducted an anti-smuggling operation in the northern regions of Kosovo, which are mainly populated by Serbs.
As many as 19 people were detained, according to Serbian President Aleksandar Vucic, who responded to the Kosovar move by ordering full alert for Serbian troops.