Tensions rose considerably in the city of Mitrovica after Kosovo declared independence on 17 February 2008. Some 150 Kosovo Serb police officers refused to take orders from the ethnic Albanian authorities and were suspended. Serb protesters prevented ethnic Albanian court employees from crossing the bridge over the Ibar River. UN police raided and seized the courthouse on 14 March using tear gas against Serbs and leaving some of them wounded. The explosion of a hand-grenade injured several UN and NATO staff on 17 March; UN forces were later withdrawn from the northern part of Mitrovica.