By Fatos Bytyci

LEPOSAVIC, Kosovo U.S. peacekeepers stood behind barbed wire as protestors held a Serbian flag outside a municipal hall in a northern Kosovo town, in an ethnically divided area where days of unrest have prompted NATO to send additional troops to stave off potential violence.

Following clashes on Monday in Zvecan, another northern town, during which 30 troops and 52 protesters were hurt, NATO said it would send 700 more troops to Kosovo to boost its 4,000-strong mission. It was not clear when the soldiers would arrive.

Polish soldiers stood guard at the town hall in Zvecan on Wednesday.

Regional unrest has intensified following April elections that the Serbs boycotted, narrowing the turnout to 3.5%, leaving victory in four Serb-majority mayoralties to ethnic Albanian candidates.

Those Albanian mayors were then installed last week, a decision that spurred rebuke of Pristina by the U.S. and its allies on Friday.

The Albanian mayor of Leposavic, who entered the building amid Serb demonstrations on Monday, remained there on Wednesday morning. He couldn't immediately be reached for comment.

"While they may have been legally elected, we do not consider their election legitimate," Dragan, an ethnic Serb who lives in Leposavic, told Reuters on Wednesday.

"We're asking what the international community is asking – for them to be removed from here peacefully," he said.

The United States and allies have rebuked Kosovo for escalating tensions with Serbia, saying the use of force to install mayors in ethnic Serb areas of Kosovo undermined efforts to improve troubled bilateral relations.

Serbian President Aleksandar Vucic placed his army on full combat alert and ordered units to move closer to the border.

Northern Kosovo's majority Serbs have never accepted Kosovo's 2008 declaration of independence from Serbia, and consider Belgrade their capital more than two decades after the Kosovo Albanian uprising against repressive Serbian rule.

Ethnic Albanians make up more than 90% of the population in Kosovo as a whole, but northern Serbs have long demanded the implementation of an EU-brokered 2013 deal for the creation of an association of autonomous municipalities in their area.

Peacekeeping troops were deployed in Kosovo in 1999 after NATO bombing drove Serbia's police and army out of its former province.

(Reporting by Fatos Bytici and Ivana Sekularac; Editing by Bernadette Baum)