Tensions between Kosovo and Serbia flared on Friday after Kosovan police arrested three ethnic Serbs, including two police officers, on suspicion of involvement in the killing of a leading Serb politician in the north of the country earlier this year.
The three men were arrested in the Serb-dominated town of Mitrovica, 40 kilometres north of the capital, Pristina, as suspects in the January slaying of Oliver Ivanovic, police said. A fourth Serb was arrested for resisting police, while a fifth person is still at large.
Police said they seized evidence for the investigation into Ivanovic's killing during raids in four locations.
A prosecutors' statement said they had found illegal weapons and other material.
Prosecutor Syle Hoxha said they have questioned more than 40 witnesses to date in the case.
The arrests triggered protests by ethnic Serbs on Mitrovica's main square.
Prime Minister Ramush Haradinaj's cabinet issued a statement calling for calm and saying that the police operation was not linked to any political development.
"I assure all citizens of the Kosovo state and the public order institutions that it [the police operation] will be never be oriented against any ethnic or political grouping," Mr Haradinaj wrote on his Facebook page.
Earlier this week, tensions soared after Kosovo failed to become a member of the international police organisation, Interpol, following intense lobbying by Serbia. Kosovo slapped a 100 per cent tax on goods imported from Serbia in apparent retaliation.
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Ethnic Serb leaders in Kosovo also called for calm and asked Serbia and the international community to assist them.
Goran Rakic, mayor of Northern Mitrovica, told Associated Press that ethnic Serb leaders had formed a crisis centre and called on the international community and Serbia for help. He said he had talked by phone with Serbian President Aleksandar Vucic.
Igor Simic, an ethnic Serb politician in Kosovo, criticised what he alleged was "excessive force" by police during the arrests.
The Serbian government is to hold an emergency session to discuss the crisis. Mr Vucic held a meeting with the commanders of army and police and security services.
He also met with the ambassadors of China and Russia, Serbia's allies in its rejection of Kosovo's independence.
Mr Vucic's adviser Nikola Selakovic said the arrests of four Serbs in Kosovo were designed to "spread fear, intimidate and demonstrate force" against the Serbs in Kosovo.
"This is a game of nerves, a walk on thin line. The goal is to provoke our reaction which would be immediately used for measures against us," Mr Selakovic said.
Kosovo's ethnic Albanians fought a bloody war with Serbia from 1998-1999 which ended with a 78-day Nato air campaign in June 1999.
Kosovo declared independence from Serbia in 2008 which Belgrade still refuses to recognise.