The man arrested on Friday after at least 87 people were killed in two separate attacks in Norway is an ethnic Norwegian and is unlikely to have links to any international terrorist organizations, RIA Novosti quoted Norway's public broadcaster NRK as saying.
The two attacks carried out late on Friday - a bomb explosion at a government headquarters in Oslo and a shooting at a youth summer camp near the capital- sparked allegations that radical Islamists or terrorist groups were behind the worst bloodshed in the country's modern history.
But police sources said a 32-year-old man, who was arrested on the Utoya island where he shot and killed at least 80 people at the Labor Party youth camp, was likely to belong to right-extremist groups in eastern Norway, the TV2 channel reported.
Terrorist attacks have been virtually unknown in Norway, the home of the Nobel peace prize and one of the world's most prosperous and stable societies.
At least seven people were killed when what seems to be a car bomb exploded on Friday afternoon at the government headquarters in central Oslo that hosts the office of Prime Minister Jens Stoltenberg. Some two dozen people were injured, but the prime minister was unharmed.
Just hours after the attack on Oslo, the gunman, disguised as a police officer, opened fire at random at the youth camp. Police have confirmed 80 deaths, saying that the figure may rise further.
A car containing explosives, which is believed to belong to the shooter, has been found on the island.
Police have not named the attacker, but some media reports identified him as Oslo resident Anders Behring Breivik and posted a picture of a blond, grey-eyed man with a small beard dressed in a black sweater over an orange shirt.
The man has been questioned by police who have also searched his house to the west of Oslo. Norwegian Justice Minister Knut Storberget said police did not know whether the man acted alone or there were others involved in the attacks.
NRK said the man, a Freemason, was active on an Islam-critical website.
According to the TV channel, the suspect was once registered to have run a company cultivating "vegetables, melons, roots and tubers" - an industry where you can also get access to large amounts of chemical fertilizers, which can be used in explosives.