Kosovo Prime Minister Albin Kurti has called for the opening of a flashpoint bridge, prompting protests, and authorities this week raided post offices long used by residents who maintain funds in Serbia.

"France firmly condemns the multiplication of unilateral actions from the Kosovo authorities in the north of the country that are affecting the daily life of the Serb community," the foreign ministry said in a statement.

"These actions endanger efforts to normalise relations with Serbia that are a prerequisite for the realisation of the European prospects of both countries," it said.

"France calls on the Kosovo authorities to refrain from any new unilateral action, which would again contribute to the escalation of tensions," the ministry added.

A NATO bombing campaign in 1999 brought self-rule to Albanian-majority Kosovo from Serbia after a war that left 13,000 dead.

Kosovo declared independence in 2008, a move never acknowledged by Serbia.

Serbia-Kosovo tensions have simmered for months following the introduction of a rule this year that made the euro the only legal currency in Kosovo and effectively outlawed use of the Serbian dinar.

The United States on Wednesday said it was "concerned by continuing uncoordinated decisions by the leadership of Kosovo".

The NATO-led peacekeeping force KFOR warned a day earlier it would intervene if Kosovo sought to reopen the bridge separating communities in the divided city of Mitrovica in northern Kosovo, the scene of frequent clashes.