SAO PAULO, Brazil (AP) _ Police killed six inmates in a gunbattle Thursday when the prisoners tried to escape a maximum security prison in northeastern Brazil.

Police killed the inmates in the early morning as they were trying to scale a 50-foot wall of the Paulo Sarazati Penitentiary near Fortaleza, 1,550 miles northeast of Sao Paulo in the state of Ceara.

``Guards saw the prisoners scale the wall with a makeshift ladder and alerted a nearby precinct,'' prison guard Joao Nicolau da Silva said by phone. ``There was a brief gunbattle that ended with six inmates dead.''

He said police would investigate how the guns used by the inmates were smuggled into the prison. No one else was hurt or wounded in the incident, he added.