Norwegian mass murderer Anders Behring Breivik returns to court on Tuesday, accusing the government of human rights violations for holding him in isolation.

He has previously compared his conditions in prison to "torture".

Breivik killed 77 people in 2011 when he bombed central Oslo before going on a shooting spree at a Labour Youth camp on the island of Utoya.

He was sentenced to 21 years in prison in 2012.

Breivik, 37, accuses the Norwegian government of breaching two clauses of the European Convention on Human Rights.

One of the clauses guarantees the right to respect for "private and family life" and "correspondence" and the other prohibits "inhuman or degrading treatment or punishment".

His lawyer, Oystein Storrvik, told AFP news agency that Breivik had been "very stressed due to his isolation" in Skien prison, about 100km (60 miles) south-west of the capital Oslo.

"One of his main things to do (in prison) was to study and he has stopped that now, and I feel that is a sign that isolation has been negative to his psychological health," he said.

Authorities say Breivik's correspondence is censored to stop him setting up an "extremist network". His visits are almost all with professionals across a glass partition.

The attorney general's office has insisted that Breivik's prison conditions are "well within the limits of what is permitted" under the convention.

The court hearing, which is being held in the gymnasium of Skien prison, is expected to run until Friday.

If the court decides that Breivik's prison conditions are so strict that they cause him harm and violate his human rights, it could order an easing of restrictions.

Last September, Breivik threatened to starve himself to death in protest at his treatment in prison.

In a letter to media outlets in Norway and Sweden, he said he was kept in almost total isolation, with time outside his cell limited to one hour a day.

He said the harsh prison conditions had forced him to drop out of a political science course at the University of Oslo.

Breivik was first held at Ila Detention and Security Prison near Oslo before being moved to Skien in 2013.

At Ila, he also complained of being held in "inhumane" conditions.

In a letter to prison authorities, he said his cell was poorly decorated and had no view. He also complained that his coffee was served cold, he did not have enough butter for his bread, and he was not allowed moisturiser.

Courtesy: BBC