The military alliance said the situation had not deteriorated but that reinforcements were needed to relieve troops currently patrolling the north.

Soldiers from Nato's Kosovo Force were deployed after clashes broke out between Kosovo police and ethnic Serbs.

The trouble began when the Kosovan government sent ethnic Albanian police to enforce a ban on Serbian imports.

A border post was torched and demolished and a Kosovo policeman killed after Serbian nationalists reacted angrily to their presence.

Previously, the border posts had been guarded by ethnic Serb police, whom the government in Pristina suspected of turning a blind eye to the ban on imports from Serbia.

The ban was imposed in response to Belgrade's effective bar on imports from Kosovo, imposed when it unilaterally declared independence from Serbia in 2008. Serbia refuses to admit any goods with a "Republic of Kosovo" customs stamp.