Photographs: Thomas Winje Oijordstret/Reuters
Many were reported wounded from the explosion in central Oslo and the shooting at a summer school meeting of Prime Minister Jens Stoltenberg's ruling Labour Party on an island outside the capital.
No group has claimed responsibility for the attacks.
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Over 80 killled in twin strikes in Norway
Photographs: Truls Brekke/Reuters
Reports of the island shooting emerged shortly after a blast tore through the government quarter in central Oslo, home to the prime minister's office, other ministries and some of the country's leading media.
Police said a "bomb" had been behind the "powerful explosion".
Stoltenberg was safe and there were no reports of other senior government officials being killed or wounded. The government was to hold a crisis meeting later today.
Over 80 killled in twin strikes in Norway
Photographs: Fabrizio Bensch/Reuters
A 32-year-old Norwegian man had been arrested over the shooting and 'is suspected of having some right-wing sympathies,' the Washington Post quoted Police Directorate spokesman Runar Kvernen as saying.
"The police are now working with the theory that he is involved in both of the tragedies today. He was observed, the same person, the same outfit, at both scenes," he said.
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Over 80 killled in twin strikes in Norway
Photographs: Per Thrana/Reuters
Witnesses reported the massive blast blew out most windows in the building as well as nearby government departments including the oil ministry, in Norway's capital and most populated city.
NATO member Norway has in the past been threatened by leaders of Al Qaeda for its involvement in Afghanistan.
Norway has been part of the International Security Assistance Force (ISAF) in Afghanistan from its foundation in late 2001.
A second theory that has been proposed behind Friday's attack is the cartoon crisis.
In early 2006, a small Norwegian newspaper had angered many Muslims by reprinting Danish cartoons depicting the Prophet Muhammad
Over 80 killled in twin strikes in Norway
Photographs: Per Thrana/Reuters
Images on Norwegian TV showed the prime minister's office and other buildings heavily damaged, sidewalks covered in broken glass and smoke rising from the area.
A police spokesman said a vehicle had been seen driving at high speed in the area just before the explosion but did not confirm that the blast had been caused by a car bomb.
Police had sealed off the area and urged residents tostay in their homes. Stoltenberg gave a telephone interview to show that he was unharmed after the deadly blast, which he called a"serious situation".
"Even if one is well prepared, it is always rather dramatic when something like this happens," he said in an interview with a Norwegian TV station.
Over 80 killled in twin strikes in Norway
Photographs: Aleksander Andersen/Reuters
European Commission president Jose Manuel Barroso voiced shock at the "abhorrent images" of the bomb blast in Oslo's government quarter.
"An attack of this magnitude is not something one would expect in Norway, famously associated with peace at home and peace-making abroad," Barroso said.
Carl Bildt, foreign minister of neighbouring Sweden, expressed solidarity with his fellow Scandinavians. "Terror has struck. We are all Norwegians," he said in a message on Twitter.
Over 80 killled in twin strikes in Norway
Photographs: Thomas Winje Oijord/Reuters
Photos posted on the NRK website showed shattered glass in front of the devastated facade of the VG building, and soldiers closing off the area and people surrounding someone apparently injured in the blast.
Last week, a Norwegian prosecutor filed terror charges against an Iraqi-born cleric for threatening Norwegian politicians with death if he's deported from the Nordic country.
The indictment centered on statements that Mullah Krekar -- the founder of the Kurdish Islamist group Ansar al-Islam made to various media, including American network NBC.
Over 80 killled in twin strikes in Norway
Photographs: Truls Brekke/Reuters
"Norway will pay a heavy price for my death," Krekar had said. "If, for example, Erna Solberg deports me and I die as a result, she will suffer the same fate."
Senior adviser Oivind Ostang told Norwegian TV2: "We can confirm that everybody who was working in the prime minister's office today are safe.
"The only thing I know is that there has been a fire or something approaching a fire in the R4-buildling which houses the oil- and energy office."
Over 80 killled in twin strikes in Norway
Photographs: Berit Roald/Reuters
Western governments lined up to condemn twin attacks in Norway, saying the "cowardly" perpetrators had shown a complete lack of humanity as they vowed to step up intelligence cooperation.
With Norway involved in both the Afghan and Libya campaigns, NATO's chief said the alliance stood united against the "heinous" acts of violence while US President Barack Obama urged countries around the world to step up cooperation in anti-terrorism efforts.
The attacks were "a reminder that the entire international community has a stake in preventing this kind of terror from occurring," Obama said during a meeting with New Zealand's Prime Minister John Key.
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