Adds quotes, details of suspect; corrects that justice minister not prime minister said suspect was Norwegian (first version posted at 08:53)
Police said early Saturday that at least 80 people were killed in an attack on a youth camp near Oslo, as Norwegian leaders expressed incomprehension over the scope of the attack, dpa reported.
The previous death toll in the shootings Friday at a political youth camp on Utoya island around 10 kilometres from the capital was given as 10.
Another seven people were killed when a bomb exploded in central Oslo in Friday's twin attacks.
Chief of police Oystein Maeland said the number of dead could rise further.
At least 25 severely injured people were flown from Utoya to Oslo hospitals.
Justice Minister Knut Storberget late Friday said a suspect arrested in connection with the shooting at the island of Utoya was a Norwegian man, but did not offer other details.
Media reports said the suspect had links to the far right and had a licence for several guns. He has expressed extremist and anti-Islamist views on some sites on the internet.
According to the online edition of newspaper VG the suspect a week ago set up a Twitter account citing British philosopher John Stuart Mill as saying, "One person with a belief is equal to the force of 100,000 who have only interests."
The 32-year-old had given some information during questioning, but Oslo police chief Sveinung Sponheim said he had not given a motive.
Police said that the current state of their investigations showed that the attacks were carried out by one person.
Witnesses at Utoya told media the suspect had worn a police uniform and "deliberately targeted" his victims.
Norway's King Harald V said Saturday that the death of the 80 young people was an "incomprehensible tragedy."
"It is important that we stick together and support each other," the monarch added.