(CNN) -- Norwegian prosecutors have asked that alleged mass killer Anders Breivik be transferred to a psychiatric institution because they believe he is mentally ill, a spokeswoman for the prosecutor's office told CNN. If that does not happen, prosecutors will ask for 21 years of prison for Breivik. Norway's Breivik gives chilling account of gun massacre . Breivik is on trial on charges of voluntary homicide and committing acts of terror in the July 22, 2011, attacks. He has admitted carrying out an attack on a youth camp on Utoya Island that killed 69 people and a bombing in Oslo that killed eight. He boasts of being an ultranationalist who killed his victims to fight multiculturalism in Norway. Last month, Breivik promised that he would not appeal if a court finds him sane and guilty.
Prosecutors say they want Breivik taken to a psychiatric institution . If not, they will ask for 21 years in prison . Breivik is on trial for attacks that killed 77 people .