|Kosovo wants its police forces to man border crossings in a region that takes its orders from Serbia [Reuters]
The European Union has condemned actions taken by Kosovo to control two contested border crossings with Serbia.
Armed Kosovo police units crossed into the Serb-run north late on Monday in an effort to place troops in a region that takes its orders from Serbia, reports the Associated Press news agency.
One member of the police unit died and four others were injured during an exchange of gunfire.
Hashim Thaci, the prime minister of Kosovo, justified the operation on Tuesday as a "concrete step in establishing the rule of law" in the north.
He said co-operation with the international community is important, but that "the constitution and the sovereignty of my country are sacred for myself and for my countrymen and go beyond any partnership or loyalty".
But at a news briefing, Maja Kocijancic, an EU commission spokesperson, described Kosovo's unilateral action in the region as "not helpful".
"It was not done in consultation neither with the European Union or the international community and we do not approve it," she said.
In Washington, President Barack Obama echoed Kocijancic's sentiments, but stopped short of a condemnation.
Though Kosovo seceded from Serbia in 2008, Serbia does not recognise its independence.
To undermine Prisitna's claim of sovereignty, Belgrade has placed its troops in the northern region and enforced a boycott against goods from Kosovo.
Pristina wants to assert control over the north and enforce a similar ban on Serbian goods.
Explaining Kosovo's position, Thaci said: "We cannot stay indifferent and tolerate forever that a part of our territory is to be a black hole not only of Kosovo but of the Europe. We cannot tolerate forever that our sovereignty is violated."
Until Monday's operation, border crossings were managed by EU police and Serbian members of the Kosovo police force.
The EU maintains a 3,000-strong "rule of law" mission in the region.
Escalation of tensions
After the operation, Kosovo says it now controls two border crossings with Serbia.
Serbia wants Kosovo's ethnic Albanian police force to pull out of the Serb-run north, leaving Serb members of the force to man the border. However, Kosovo refuses - as Serbian members do not obey orders from Pristina.
The impasse has resulted in an escalation of tensions.
Reports of skirmishes and exchanges of gunfire between Pristina's police force and local Serbs were reported on Tuesday, but could not be confirmed.
Thaci said he wanted to make it clear that Kosovo's move was not an act of war.
The action that we undertook last night under no circumstances should be considered as a hasty move and with intention of provocation," he said.
"In fact, the only objective was and is to establish law and order."