WASHINGTON - A senior aide to U.S. President Joe Biden expressed concern about events in northern Kosovo in calls with Prime Minister Albin Kurti and Serbian President Aleksandar Vucic, the White House said on Friday.

A political crisis that has spiraled into violence in Kosovo's north has intensified since ethnic Albanian mayors took office in the region's Serb-majority area, a move that led the U.S. and its allies to rebuke Pristina. The majority Serb population had boycotted the April election, allowing ethnic Albanians to be elected.

On Thursday, Biden's principal deputy national security adviser, Jon Finer, spoke with Kurti and called for Kosovo "to enable newly elected mayors to carry out their duties from alternative locations and to withdraw police forces from municipal buildings," the White House said.

He also welcomed "Kurti's willingness to work towards conditions for new elections," it said.

The Biden aide spoke with Vucic on Friday and pushed for Serbia to "to withdraw its armed forces stationed near the border and to lower their state of readiness, as well as to urge protesters to remain peaceful in northern Kosovo," according to the U.S. summary of the call.

In both calls, the White House said Finer expressed concern about the situation and pushed for all parties to reduce conflict. Washington also expected both sides to re-engage in a European Union dialogue and "to fully implement the normalization agreement" reached earlier this year.

In violence on Monday, 30 peacekeepers and 52 Serbs who protested against the installation of ethnic-Albanian mayors were injured. The violence prompted NATO to announce it would send additional troops on top of 700 already on their way to the Balkan country to boost its 4,000 strong mission.

The presidents of Serbia and Kosovo insisted on Thursday that they want to defuse the crisis but have shown little sign of backing down from their opposing positions.

  - Reuters