The United States, NATO and the European Union have called for maximum restraint in northern Kosovo, where authorities have closed a third border crossing point amid a worsening dispute with local Serbs.

 "We call on everyone to exercise maximum restraint (and) take immediate action to de-escalate the situation unconditionally," the EU and U.S. said in a joint statement.

NATO's mission in Kosovo, KFOR, said it supports dialogue between all sides to defuse tensions.

Serbia put its army on high alert earlier this week.