OSLO (AFP) - The suspect in Norway's twin attacks that killed at least 92 people says he acted alone, police said Sunday, after some witness accounts said a second gunman had taken part in a mass shooting.

But police are still trying to establish whether there was "one or several" shooters at Friday's attack on a Labour Party youth meeting on Utoeya island, northwest of Oslo, police commissioner Sveinung Sponheim told journalists.

Anders Behring Breivik, 32, was arrested for allegedly shooting at least 85 people dead at a youth Labour Party meeting on an island and killing seven more in a car bomb explosion which ripped through government buildings in Oslo.

"He admitted responsibility," Behring Breivik's lawyer Geir Lippestad told Norway's NRK television channel. While there was no official confirmation of the man's identity, he was widely named as Anders Behring Breivik by local media.

"He explained that it was cruel but that he had to go through with these acts," Lippestad said, adding that the attacks were "apparently planned over a long period of time".