European Union foreign affairs chief Javier Solana has condemned the murder of a Serb teenager in Kosovo, amid fears of fresh ethnic tensions.
Solana says the reconstruction process has been slow
Two ethnic Albanians have been arrested in connection with the shooting.
Speaking as he visited areas destroyed by ethnic violence in March, Mr Solana also criticised Kosovo Albanian leaders for delays to rebuilding of Serb homes.
He warned that the EU would intervene if the authorities did not finish the reconstruction work by September.
The teenager killed early on Saturday was 16-year-old Dimitrije Popovic, who was shot dead at an outdoor fast food stall in the town of Gracanica, 15km (8 miles) south of Pristina.
Police set up checkpoints in a bid to stop a fresh spiral into anarchy. They also stepped up patrols, backed up by Nato-led peacekeepers, who have been in the province under a UN mandate since 1999.
Around 800 homes were destroyed and 19 people killed during clashes between Serbs and ethnic Albanians earlier this year.
Mr Solana received a hostile reception when he visited Kosovo after the ethnic violence in March which left 19 dead.
On Monday, he returned to the ethnically mixed town of Kosovo Polje where schools and homes were burned down.
He said the government-led efforts for reconstruction in the Serb-populated areas had been too slow.
"Some effort has been done. But the speed at which the process of reconstruction is going is too slow," he said.
Call for calm
Referring to the teenager's death, he added: "A society where kids of 16 years are killed is not a healthy society.
"That society does not belong to Europe. I don't know where it belongs."
Mr Solana is expected to meet ethnic Albanian Prime Minister Bajram Rexhepi to discuss the aftermath of the March violence.
Hundreds of Serb families were forced to leave their homes in March
The BBC's Matt Prodger, in Belgrade, says the killing comes at a time of high tension in Kosovo, with many fearing that further outbreaks of violence in the province are imminent.
Kosovo's leading Albanian politicians condemned the killing and pleaded for restraint.
"I call on all citizens to remain calm," said Mr Rexhepi, adding that the killers would be brought to justice.
It is not yet known why the teenager was killed.
Clashes between Serb and ethnic Albanians communities broke out in March, forcing many Serb families to flee the province as Albanian mobs attacked their homes.
Kosovo's UN administrator, Harri Holkeri, announced he was stepping down not long afterwards; a successor has yet to be appointed.
Kosovo's Serb and Albanian communities have been locked in an uneasy stand-off since a Nato bombing campaign drove Serbian security forces out of the province and drew it under UN control.
The Belgrade government, then under Slobodan Milosevic, was accused of war crimes against Kosovo's Albanian Muslims, who had been agitating for independence from Serbia.
Lingering hostility between the two communities have hampered international efforts to repair ethnic relations and reach a final settlement on the province's status.