Anders Behring Breivik
Anders Behring Breivik killed 77 people in Norway 2011 in one of the worst terrorist attacks in Europe Odd Andersen/AFP

Norwegian mass murderer Anders Breivik has threatened to starve himself to death in protest at his treatment in prison. Breivik, who killed 77 people during a bomb attack and mass shooting in 2011, claims he has been kept in isolation since 2 September and is only allowed to leave his cell for one hour a day.

In an open letter sent to Norwegian and Swedish media, Breivik says the conditions are getting worse and his communications with prison staff have now been limited to speaking through a small gap in the door. Breivik is currently serving 21 years in jail after killing eight people in a bomb attack in Oslo before going on to kill a further 69 at a political youth camp in Utoya.

In the letter, seen by The Local, Breivik wrote: "Unless the 02/09/15 escalation [sic] is reversed, I will eventually continue the hunger strike until death. I cannot stand any more."

He complained the conditions mean he is no longer able to continue studying his political science course at University of Oslo. He added: "Studying and corresponding is not humanly possible under such circumstances, and this applies to anyone who is isolated under such conditions.

"The decision about the drastic deterioration of prison conditions forced me to drop out of my studies, which in turn means that I will lose my place at the university. The studies, which were made possible for only thirteen full days before the Minister of Justice put an end to them, were the only thing I had."

Brevik previously threatened to go on hunger strike in 2014 if the prison he was being held in did not update the PlayStation 2 games console with a PlayStation 3 and demanded he be allowed to choose "more adult games" to play.