Mass killer Anders Behring Breivik opened a court case against Norway on Tuesday with a Nazi salute as his lawyers prepared to argue he has received inhuman treatment by being kept in isolation for murdering 77 people in 2011.Appearing in public for the first time since he was sentenced in 2012, Breivik has had just one visitor with whom he had physical contact - his mother, who was allowed into prison and gave him a hug shortly before she died of cancer in 2013.Clean-shaven and wearing a black suit, white shirt and golden tie, Breivik raised his right arm in a flat-handed Nazi salute on arrival at the court, slightly different from the outstretched arm and clenched fist he used in 2012.Breivik's lawyer accused Norway of violating a ban on "inhuman and degrading treatment" under the European Convention on Human Rights by keeping the 37-year-old isolated from other inmates in a special three-room cell."There is no tradition in Norway for this type of isolation," lawyer Oeystein Storrvik told the special court that will meet until Friday in a gymnasium at Skien jail about 100 km (60 miles) south of Oslo.Storrvik told Reuters he had advised Breivik against making the Nazi salute. "He (Breivik) says he is a national socialist," he said, adding that making the gesture was "the worst thing you can do in a courtroom."Norway rejects the charges of inhuman treatment."Breivik is a very dangerous man," said Marius Emberland, the lawyer representing the state, defending Breivik's conditions.He said another prisoner tried to attack Breivik last year, getting to within earshot. When stopped by guards, the man shouted: "You are a killer, a child killer ... And I love my country," Emberland said.Breivik killed eight people with a bomb in Oslo and gunned down 69 others on an island nearby, many of them teenagers. He is serving Norway's maximum sentence of 21 years, which can be extended.Breivik will have a chance to speak on Wednesday. The single judge - there is no jury - will issue a ruling in coming weeks.Norway considered it too dangerous to hear the case in Oslo. The makeshift courtroom has walls lined with timber bars and a climbing frame as well as two basketball hoops.Some survivors watched the trial in an Oslo court with a direct transmission by television. Most stayed away, not wanting to revive memories of July 22, 2011.