Acting Police Chief Sveinung Sponheim told broadcaster NRK that investigators suspect the bombing was linked to a shooting spree at the Labor Party's youth camp later Friday by a gunman in a police uniform.
Prime Minister Jens Stoltenberg has urged Norwegians to not cave in to fear. Stoltenberg told Norwegian broadcaster NRK: "Co-workers have lost their lives today ... "it's frightening. That's not how we want things in our country. But it's important that we don't let ourselves be scared. Because the purpose of that kind of violence is to create fear."
There was no claim of responsibility, though NATO member Norway has been the target of threats, if not bombs, before, notably over its involvement in conflicts in Afghanistan and Libya. Prime Minister Jens Stoltenberg was safe, NTB said.
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.
“So far I can confirm that we have received seven people at Oslo University Hospital,” a press officer at the clinic said.
“I don’t know how seriously wounded they are.”
The explosion blew out most of the windows of the 17-story central government building, cast a huge pall of smoke over the city and scattered shards of metal and other debris for hundreds of meters.
Nearby ministries were also hit, including the oil ministry, which was on fire. Heavy debris littered the streets.
John Drake, senior risk consultant, at London-based consultancy AKE said: “It may not be too dissimilar to the terrorist attack in Stockholm in December which saw a car bomb and secondary explosion shortly after in the downtown area.
“That attack was later claimed as reprisal for Sweden’s contribution to the efforts in Afghanistan.”
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, as well as the damage to the buildings, appeared consistent to witnesses with that from car bombs.
The United States has expressed its sympathy to the Norwegian government over the Oslo bombing and offered aid, but so far Norway has not requested help.
NATO member Norway has sometimes in the past been threatened by leaders of Al-Qaeda for its involvement in Afghanistan. But political violence is virtually unknown in a country known for sponsoring the Nobel Peace Prize and mediating in international conflicts, including in the Middle East and Sri Lanka.
It has also taken part the NATO bombing of Libya, where Muammar Qaddafi has threatened to strike back in Europe.
David Lea, Western Europe analyst, at Control Risks said: “There certainly aren’t any domestic Norwegian terrorist groups although there have been some Al-Qaeda-linked arrests from time to time. They are in Afghanistan and were involved in Libya, but it’s far too soon to draw any conclusions.”
