Twin shooting and bomb attacks left at least 91dead in western Europe's deadliest carnage since the 2004 Madrid bombings as a Norwegian gunman opened fire at a youth camp and a bomb tore through central Oslo.

The suspect was a 32-year-old Norwegian who posted anti-Muslim rhetoric online, police commissioner Sveinung Sponheim told the NRK television channel, but added: "It's too early to say if this was a motive behind the act."

Norwegian Public Radio identified the suspect as Anders Bering Breyvik, blond, blue-eyed Norwegian who has expressed anti-Muslim right-wing views on the Internet.

The man is legally owned several firearms, and was a member of a shooting club. He has owned agricultural company for growing vegetables, which would give him access to large amounts of manure, a potential ingredient in creating bombs.

Police voiced fears that the toll could rise as they searched for victims of the shootings at a summer school meeting organised by Prime Minister Jens Stoltenberg's ruling Labour Party on Utoeya, an island outside the capital. Bomb sniffing dogs were used on the island after the man's arrest, and discovered two devices.

Security was meanwhile tightened across potential target sites in the capital, police said Saturday, but they lifted an advisory that had urged residents to stay home.

Norway PM: "Youth paradise turned into hell"

Norway's Prime minister has described how his "childhood paradise has been transformed into hell" after a guman killed at least 84 people at a summer youth camp.

Jens Stoltenberg said he had spent many summers on the island of Utoya - where 32-year-old Anders Behring Breivik is alleged to have gone on a shooting spree.

"Never since the Second World War has our country been hit by a crime on this scale," he said.

He described the attacks as a "national tragedy"

Claim responsibility via Jihadi forums

Terrorists responsible for today's attacks in Oslo, Norway have claimed responsibility via social media.

An obscure group called Ansar al-Jihad al-Alami (Assistants of the Global Jihad) posted a message on an Islamist bulletin board called Smukh and may have uploaded a video to YouTube weeks ago several days ago in which they predicted the attack.

Ansar al-Jihad's Abu Sulayman al-Nasir allegedly posted a message claiming responsibility for the Oslo attacks on the Arabic-language jihadist forum Shamikh. According to a partial translation by terrorism expert Will McCants of Jihadica, al-Nasir claims the attacks were in retribution for the occupation of Afghanistan by foreign troops and unnamed insults to the Muslim prophet Muhammad. Al-Nasir also threatens further attacks:

We have warned since the Stockholm raid of more operations and we have demanded that the countries of Europe withdraw from the land of Afghanistan and end their war on Islam and Muslims. What you see is only the beginning and there is more to come.

The “Stockholm raid” reference is in response to a 2010 suicide bombing in Sweden.

A huge bomb devastated the main government building in Norway's capital Oslo on Friday, and state radio said two people were killed and several others wounded.

Though the attack was on the very heart of power in the small Nordic state, Prime Minister Jens Stoltenberg was safe. There was no claim of responsibility.

The Oslo blast tore at the facade of the 17-story central government building, blowing out most of the windows and scattering shards of metal and other debris for hundreds of meters (yards).

NRK state radio said at least two people were killed while another station, NTB, quoted a police chief as confirming it was a bomb.

A Reuters reporter at the scene said the blast scattered debris across the streets and shook the entire city center around 3:30 p.m. (1330 GMT). He saw eight people injured, one covered in a sheet and apparently dead.

The Reuters correspondent said the streets had been fairly quiet in mid-afternoon on a Friday in high summer, when many Oslo residents take vacation or leave for weekend breaks.

The tangled wreckage of a car was outside one building. This, as well as the damage to the buildings, appeared to witnesses to be consistent with a car bomb.

The district attacked is the very heart of power in Norway, with several other key adminstration buildings nearby.

Nearby ministries were also hit by the blast, including the oil ministry, which was on fire. Nevertheless, security is not tight given the lack of violence in the past.

Not long after a bomb ripped through government buildings, there are reports of a shooter at a camp put on by the ruling labor party.

The camp is on the island of Utoya.