The Kosovo government said on Friday that a Russian national working for the UN mission would not be allowed back into the country after his expulsion.
It said the UN staffer, Mikhail Krasnoshchenkov, had been declared persona non grata. The UN mission, UNMIK, said on Thursday the Russian had sustained injuries when he was arrested during a police anti-crime operation in Kosovo and was now in a Belgrade hospital.
The expulsion has added further strains to the difficult relationship between Kosovo and Serbia, which used to rule Kosovo. The small state, which has an ethnic Albanian majority and Serb minority, declared independence in 2008. A decade earlier NATO air strikes had wrested control of Kosovo away from Serbia to end a Serb counter-insurgency campaign.
On Tuesday, Kosovo police arrested 19 police officers, 11 of whom were Serbs. They were accused of smuggling and other illegal activities in the volatile north of the country.
Belgrade, which says the operation was a show of force against Serbs, has put its police and army units on highest alert in response.
During a police operation in Kosovo, a Russian national and a local UN colleague, both employed in the United Nations mission in Kosovo (UNMIK) office, had been detained shortly and later released. The Kremlin called the arrest of the Russian national a "flagrant incident."
Police said the two UN employees had been arrested for standing on a barricade set up by local Serbs to stop police vehicles from passing.
"The decision was taken today. This person who works as an international staff for the United Nations ... was ordered to leave the territory of the republic of Kosovo," Kosovo Prime Minister Ramush Haradinaj wrote on his Facebook page.
"The decision was taken because of the actions of the Russian national against Kosovo's constitutional order..." he wrote.
The UN mission was set up to run Kosovo following the end of the 1998-99 war, but it lost executive mandate when Kosovo declared independence in 2008.