Norwegian mass murderer Anders Behring Breivik has threatened to starve himself to death in protest at his treatment in prison, according to media reports.
Breivik claims to have been kept in isolation since 2 September, with time outside his cell limited to an hour a day.
Breivik killed 77 people in 2011 when he bombed central Oslo before going on a shooting spree at a youth camp.
He was sentenced to 21 years in 2012.
His claims about deteriorating prison conditions were made in a letter to media outlets in Norway and Sweden.
In his letter, Breivik, 36, says harsh prison conditions have forced him to drop out of a political science course at the University of Oslo.
"Studying and corresponding is not humanly possible under such circumstances, and this applies to anyone who is isolated under such conditions," he wrote according to English news site The Local.
Breivik said that if conditions remained unchanged he would continue the hunger strike until he died, Norwegian media reported.
No one at Skien prison, where Breivik is held, is currently on hunger strike, prison director Ole Kristoffer Borhaug told the BBC.
He declined to comment on the conditions of individual prisoners.
Norwegian Justice Minister Anders Anundsen also declined to comment on Breivik's claims, according to the Dagbladet newspaper.
The University of Oslo admitted Breivik as a full student in July, explaining that inmates had a right to higher education if they won entry to courses.
Breivik has previously complained of "inhumane" prison conditions, including that his coffee was being served cold.