 Other Serb-dominated communities in eastern Croatia announced that they would also join SAO Krajina and ceased paying taxes to the Zagreb government.On Easter Sunday, 31 March 1991, the first fatal clashes occurred when Croatian police from the Croatian Ministry of the Interior (MUP) entered the Plitvice Lakes national park to expel rebel Serb forces.Serb paramilitaries ambushed a bus carrying Croatian police into the national park on the road north of Korenica, sparking a day-long gun battle between the two sides.