Police say at least nine people have been killed at a Brazilian penitentiary in a clash between rival gangs of inmates in the northern state of Roraima.

The state's justice secretary Uziel Castro says in a statement that seven bodies were piled up and burned after the Sunday prison mutiny. Two other bodies were found in a different part of the Monte Cristo prison. Castro says at least three of the bodies were beheaded and efforts to identify them have been slow.

Officers said Monday that about 50 people who were visiting the penitentiary in the state on the border with Venezuela and Guyana were released unharmed after being held hostage.