Right-wing extremist Anders Behring Breivik pleaded not guilty to charges he committed "acts of terror" when he massacred 77 people in twin attacks in Norway last July.

Defendant Norwegian mass killer Anders Behring Breivik waits for his terrorism and murder trial to start, in a courtroom in Oslo April 16, 2012. , Photo: Reuters

"I acknowledge the acts, but not criminal guilt and I claim self-defence," he told the court on the first day of his 10-week trial.

The judge then entered the plea as "not guilty."

His plea came after prosecutor Inga Bejer Engh spent over an hour reading the charges against him, including "acts of terror," and listing each of his 77 victims and and how they died.

Breivik, 33, has described his actions as "cruel but necessary" and claims he acted alone and in self-defence against those he considered to be "state traitors" for opening Norway up to multiculturalism and allowing the "Muslim invasion" of Europe.

On July 22, Breivik killed eight people when he set off a bomb in a van parked at the foot of government buildings in Oslo housing the offices of Labour prime minister Jens Stoltenberg, who was not present at the time.

He then travelled to Utoeya island outside Oslo where, dressed as a police officer, he spent more than an hour methodically shooting at hundreds of people attending a Labour Party youth summer camp.

The shooting spree left 69 people dead, most of them teenagers trapped on the small heart-shaped island surrounded by icy waters, and is the deadliest massacre ever committed by a sole gunman.

Anders Behring Breivik welled up in tears as the court viewed a film he posted online the day of the attacks.

His face red with emotion, Breivik's lips trembled and he wiped away tears as the 12-minute film was projected on a large screen, including photos and drawings of Islamists.

Source: AFP