Kosovo wants its police forces to man border crossings in a region that takes its orders from Serbia [Reuters]

Ethnic Serbs have set fire to a border crossing post in northern Kosovo after Kosovo's government said it had regained control of the post and a second one, officials said.

Oliver Ivanovic, Serbia's state secretary for Kosovo, said no one was hurt in Wednesday's incident but voiced concerns about further violence.

"One act of violence produces more violence. I am afraid we are entering a spiral of violence," he told the Reuters news agency.

Armed ethnic Serbs also fired at NATO peacekeeping forces in Kosovo on Wednesday in the ethnic-Serb dominated northern part of the country.

"The situation deteriorated at the customs post Jarinje and it was confirmed that an act of arson was committed against that position," NATO peacekeeping mission in Kosovo (KFOR) said in a statement. 

"There have also been confirmed reports of shots fired at KFOR personnel in the vicinity," the statement added.

The NATO statement did not say whether anyone was injured in the attack or whether KFOR troops returned fire, but said reinforcements had been sent to the border.

Kosovo raid

On Monday, armed Kosovo police units crossed into the Serb-run north in an effort to station troops in a region that takes its orders from Serbia, the Associated Press news agency said.

A Kosovo police officer was shot in the head and died on Tuesday and four others were injured during an exchange of gunfire between police and local Serbs opposing Kosovo's efforts to take control of its border posts.

The same border post was burned down in 2008 by local Serbs after Kosovo declared independence.

Earlier, the European Union condemned Kosovo's actions to control the two contested border crossings with Serbia.

Hashim Thaci, the prime minister of Kosovo, justified the operation on Tuesday saying it was a "concrete step in establishing the rule of law" in the north.

He said co-operation with the international community was 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".

Not helpful

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 nor the international community and we do not approve it," she said.

In Washington, President Barack Obama echoed Kocijancic's sentiments, but stopped short of condemning Kosovo.

Though Kosovo seceded from Serbia in 2008, Serbia does not recognise its independence.

To undermine Kosovo's claim of sovereignty, Serbia has stationed its troops in the northern region and enforced a boycott against goods from Kosovo.

Kosovo wants to assert control over the north and enforce a similar ban on Serbian goods.