The parliament in Kosovo has angered Serbia by voting to establish a new regular army.
Belgrade has responded by saying armed intervention in its former province is one option on the table. while NATO has deplored the move as "ill timed".
Serbia's president Aleksandar Vucic hit out at America, who he blamed for allowing the formation of a Kosovo army. The breakway state, not universally recognised, currently has a 4,000 strong Security Force. The plan is to replace it with a similarly-lightly-armed 5,000 strong army, with 3,000 reservists.
Extra NATO troops have been deployed on a bridge in Mitrovica, often a flashpoint in a divided town in northern Kosovo with a significant Serb community, in anticipation of trouble.