In Bolivia, a bomb blast has killed four people during carnival celebrations in the city of Oruro. <br/><br/>Police said a device packed with three kilograms of dynamite exploded late last night, killing bystanders. <br/><br/>Army units patrolled the streets of the city after the blast. <br/><br/>Regional Governor Victor Hugo Vasquez said it was a criminal attack. Three suspects have been arrested. <br/><br/>The city's university and schools located near the incidents remained closed.