Last Updated 1:51 p.m. ET
OSLO, Norway A powerful bomb tore into the heart of Norway on Friday, killing seven people and injuring many others as it ripped open buildings including the prime minister's office. It was the deadliest bombing ever in Oslo, normally associated with the Nobel Peace Prize that is awarded there.
Police confirmed that the explosion was caused by "one or more" bombs. Broadcast NRK showed video of a blackened car lying on its side amid the debris. Police told local media that seven people were killed.
A senior adviser to Prime Minister Jens Stoltenberg said Stoltenberg was working at home Friday and was not in the building.
A U.S. State Department spokesperson said the United States condemned the "despicable acts of violence.
About an hour later, a man dressed in a police uniform opened fire at a summer youth camp on an island where a former prime minister was due to speak today. Reports say several people were injured, and panic spread as people are trapped on Utoya, an island in Tyrifjorden.
One man was arrested; there were unverified reports that four people were killed.
BBC News reports that Norwegian police say they believe the two incidents are connected.
The office of broadcaster TV2 has been sealed off because of a suspicious package.
Most of the windows in the 20-floor high rise were blown out, and the bottom floor appeared to be gutted. Nearby offices were also heavily damaged and evacuated, including those housing some of Norway's leading newspapers and news agency NTB.
Emergency crews are trying to rescue people trapped in damaged buildings, although the number of those trapped is unknown.
Norwegian news agency NTB says police confirm the Oslo explosion was caused by a bomb.
"There has been one or several powerful explosions in the government district in Oslo," Oslo police said in a brief statement.
AFP reports Norwegian police are telling Oslo residents to stay at home. "It is necessary to avoid big gatherings, to go back home," a police officer is quoted as saying. "It is wise to stay at home."Witness Ole Tommy Pedersen was standing at a bus stop about 100 yards from the high-rise at around 3:30 p.m. (1330 GMT) when the explosion occurred.
"I saw three or four injured people being carried out of the building a few minutes later," Pedersen told AP.
Craig Barnes was in his car driving away from a restaurant when he heard a loud explosion behind him, and as he turned to look, the sky had turned gray. "It's total chaos," Barnes told CBS News.
Believing it to be a terrorist bomb in an area dominated by government buildings, Barnes said he "put his foot down" on the gas to get out of town as fast as he could.
An AP reporter who was in the NTB office said the building shook from the blast and all employees evacuated as the alarm went off. Down in the street, he saw one person with a bleeding leg being led away from the area.
The government building houses the offices of the prime minister and his administration. Several ministries are in surrounding buildings.
Because it is a holiday in Norway the capital is less crowded than it might otherwise have been, and many workers would already have left by the time the late Friday afternoon blast occurred.One witness named Saskia, who was a few blocks from the blast, told BBC News that the blast was like an earthquake: "It is so shocking for such a normally calm and relaxed city."
The blast comes as Norway grapples with a homegrown terror plot linked to al Qaeda. Two suspects are in jail awaiting charges.
Last week, a Norwegian prosecutor filed terror charges against an Iraqi-born cleric for threatening Norwegian politicians with death if he is deported from the Scandinavian country. The indictment centered on statements that Mullah Krekar the founder of the Kurdish Islamist group Ansar al-Islam made to various news media, including American network NBC.
Terror expert John Bew told CBS Radio News says the attack could very well have been carried out by al Qaeda: "Norway has already been a target for al Qaeda-related terrorism, and there have been international plots focused there."
Terrorism has also been a concern in neighboring Denmark since an uproar over cartoons of the Prophet Muhammad six years ago. Danish authorities say they have foiled several terror plots linked to the 2005 newspaper cartoons that triggered protests in Muslim countries. Last month, a Danish appeals court on Wednesday sentenced a Somali man to 10 years in prison for breaking into the home of the cartoonist.