Norwegian mass killer Anders Behring Breivik, who has legally changed his name to Fjotolf Hansen, has filed an appeal to the European court of human rights against his prison conditions, his lawyer was quoted as saying on Thursday.

Earlier this month, the Norwegian Supreme Court declined to take up an appeal lodged by the anti-Muslim far-right extremist, who killed 77 people in Norway's worst peacetime atrocity in July, 2011.

One of his lawyers, Oeystein Storrvik, had said at the time that he would file an appeal to the European Court of Human Rights in Strasbourg.

"The essence of our complaint is that we protest against the excessive level of isolation and that this isolation has taken place for a long time," Storrvik told state broadcaster NRK.

Breivik is seeking to overturn a March decision by a Norwegian appeals court that ruled that his near-isolation in a three-room cell respected human rights. (Reporting by Gwladys Fouche, editing by Ed Osmond)