BRUSSELS, Belgium — The European Union urged Serbia and Kosovo on Friday to reduce tensions after a series of incidents on their border.

EU foreign policy chief Catherine Ashton said Robert Cooper, the bloc's mediator, would visit the region in coming days to get the two sides back to the negotiating table.

One policeman died this week after Kosovo police tried to seize control of border crossings with Serbia. The action was not co-ordinated with EU police or NATO's peacekeeping troops stationed in Kosovo. A Serbian mob then attacked the police and later torched one of the crossings.

NATO has deployed U.S. and French troops to prevent further violence. The alliance still keeps about 5,000 troops in Kosovo, a former Serbian province, 12 years after the war that ended Serbia's rule over it. The EU has a police mission numbering about 650 officers.

"I urge both Pristina and Belgrade to take the full measure of what is at stake, show maximum restraint, avoid further escalation and engage constructively with a view to finding a peaceful, negotiated solution without further delay," Ashton said.

Kosovo declared independence from Serbia in 2008. Serbia has said it will never recognize the new state and Serbs living in Kosovo's north do not recognize the authority of Pristina, Kosovo's capital, over them.

Kosovo's statehood is recognized by more than 70 nations, including the United States and most EU members.

Kosovo has been blocked from joining the United Nations, most of whose members have not recognized it despite intense lobbying by Washington. It also remains in limbo within the EU because five member states have refused to recognize it.

The EU initiated the first direct negotiations between the two sides in March. The talks resulted in a breakthrough in June, when Serbia and Kosovo decided to simplify border procedures, recognize each other's school diplomas and resolve other practical issues.

The talks have so far not touched on more substantive issues such as mutual recognition. The EU sees the continuing dialogue as a key condition for Serbia to join the 27-nation bloc.