ZVECAN, Kosovo (AP) — Troops from the NATO-led peacekeeping force in Kosovo on Wednesday placed metal fences and barbed wire barriers in a northern town following clashes with ethnic Serbs that left 30 international soldiers wounded.

Hundreds of ethnic Serbs began gathering in front of the city hall in Zvecan, 45 kilometers (28 miles) north of the capital, Pristina, in their repeated efforts to take over the offices of one of the municipalities where ethnic Albanian mayors took up their posts last week.

NATO has decided to send 700 more troops to northern Kosovo to help quell violent protests after the clashes on Monday.

The confrontation unfolded last week after ethnic Albanian officials who were elected in a vote overwhelmingly boycotted by Serbs entered municipal buildings to take office. When Serbs tried to block them, Kosovo police fired tear gas to disperse them in Zvecan, leading to clashes with NATO-led troops that left 30 international soldiers injured.

NATO peacekeepers have insisted that both ethnic Albanian mayors and Kosovo police must leave northern Kosovo.

Serbia put the country’s military on the highest state of alert and sent more troops to the border with Kosovo.

A former province of Serbia, Kosovo’s 2008 declaration of independence is not recognized by Belgrade. Ethnic Albanians make up most of the population, but Kosovo has a restive Serb minority in the north of the country bordering Serbia.