http://www.b92.net/eng/news/crimes-article.php?yyyy=2008&mm=02&dd=15&nav_id=47721

It appears that valiant Serbian WNs are at work:

"...A powerful blast was heard in northern Kosovska Mitrovica around 22:30 CET last night... His property borders with a building housing the local headquarters for a planned EU mission to Kosovo..."

A thorough report here (up 'til now, anything in English is brief):

http://www.lemonde.fr/europe/article/2008/02/15/kosovo-une-explosion-a-mitrovica-fait-de-legers-degats-materiels_1011637_3214.html#ens_id=979287

The explosion only shattered a couple windows and reportedly didn't injure anyone. It took place in the Serbian half of the city, in the north, and detonated close to the residence of the EU delegation.
Too bad they couldn't make it count