Last Updated 8:29 p.m. ET
OSLO, Norway - A home-grown terrorist set off an explosion that ripped open buildings in the heart of Norway's government Friday, then went to a summer camp dressed as a police officer and gunned down youths as they ran and even swam for their lives, police said Friday.
The attacks killed at least 16 people in this peaceful nation's worst violence since World War II.
A police official said the 32-year-old ethnic Norwegian suspect arrested at the camp on Utoya island appears to have acted alone in both attacks, and that "it seems like that this is not linked to any international terrorist organizations at all." The official spoke on condition of anonymity because that information had not been officially released by Norway's police.
"It seems it's not Islamic-terror related," the official said. "This seems like a madman's work."
The official said the attack "is probably more Norway's Oklahoma City than it is Norway's World Trade Center." Domestic terrorists carried out the 1995 attack on a federal building in Oklahoma City, while foreign terrorists were responsible for the Sept. 11, 2001 attacks.
The official added, however, "it's still just hours since the incident happened. And the investigation is going on with all available resources."
TV2 Norwegian TV reported that the shooting suspect in custody has links to right wing extremism
At the youth camp, where the prime minister had been scheduled to speak Saturday, a 15-year-old camper named Elise said she heard gunshots, but then saw a police officer and thought she was safe. Then he started shooting people right before her eyes.
"I saw many dead people," said Elise, whose father, Vidar Myhre, didn't want her to disclose her last name. "He first shot people on the island. Afterward he started shooting people in the water."
Elise said she hid behind the same rock that the killer was standing on. "I could hear his breathing from the top of the rock," she said.
She said it was impossible to say how many minutes passed while she was waiting for him to stop.
The shooting occurred after the bombing in Oslo, Norway's capital and the city where the Nobel Peace Prize is awarded. The blast left a square covered in twisted metal, shattered glass and documents expelled from surrounding buildings in a dust-fogged scene that reminded one visitor from New York of Sept. 11.
"People were just shocked like, as if to say, 'What was that?'," Craig Barnes said on the CBS Evening News, "because they never experienced anything like this ever in Oslo, or even Norway."
Ian Dutton, who was in a nearby hotel, said people "just covered in rubble" were walking through "a fog of debris."
"It wasn't any sort of a panic," he said, "It was really just people in disbelief and shock, especially in a such as safe and open country as Norway. You don't even think something like that is possible."
According to CBS News, government workers traditionally on a Friday are allowed to leave early at 3pm for the weekend. Investigators speculate that the bomb may have been intended to inflict big casualty damage at that time.
Police said seven people died in the Oslo blast, and another 9 or 10 people were killed at the camp, which was organized by the youth wing of the ruling Labor Party. Rescuers were to search to blast wreckage through the night for more victims, and Prime Minister Jens Stoltenberg said police fear there could be more victims at the camp as well.
Elise, the young camper, said she believes she saw more than 10 people killed.
Acting national Police Chief Sveinung Sponheim said a man was arrested in the shooting, and the suspect had been observed in Oslo before the explosion there. Police did not immediately say how much time elapsed between the bombing and the attack at Utoya, about 20 miles (35 kilometers) northwest, but reports of the shooting began appearing on Twitter about two and a half hours after the bombing.
Sponheim said the camp shooter "wore a sweater with a police sign on it. I can confirm that he wasn't a police employee and never has been."
Aerial images broadcast by Norway's TV2 showed members of a SWAT team dressed in black arriving at the island in boats and running up the dock. Behind them, people who stripped down to their underwear swam away from the island toward shore, some using flotation devices.
Sponheim said police were still trying to get an overview of the camp shooting and could not say whether there was more than one shooter. He said several people were injured but he could not comment on their conditions.
In Oslo, most of the windows in the 20-floor high-rise where Stoltenberg and his administration work were shattered. Other buildings damaged house government offices and the headquarters of some of Norway's leading newspapers. and that rescuers were to search damaged buildings through the night for more victims.
Oslo University Hospital said 12 people were admitted for treatment following the Utoya shooting, and 11 people were taken there from the explosion in Oslo. The hospital asked people to donate blood.
Stoltenberg, who was home when the blast occurred and was not harmed, decried he called "a cowardly attack on young innocent civilians."
"I have message to those who attacked us," he said. "It's a message from all of Norway: You will not destroy our democracy and our commitment to a better world."
Sponheim would not give any details about the identity or nationality of the suspect, who was being interrogated by police.
Stoltenberg said "we don't want to speculate" on whether a terror group is responsible, and said some groups may take responsibility "to appear to be more important than they are."
The attacks formed the deadliest day of terror in Western Europe since the 2005 London bombings, which killed 52 people.
Police said the Oslo explosion occurred at 3:30 p.m. (1330 GMT) and was caused by "one or more" bombs, but declined to speculate on who was behind the attack. They later sealed off the nearby offices of broadcaster TV 2 after discovering a suspicious package.
Public broadcaster NRK showed video of a blackened car lying on its side amid the debris. An AP reporter who was in the office of Norwegian news agency NTB said the building shook from the blast and all employees were evacuated. Down in the street, he saw one person with a bleeding leg being led away from the area.
An AP reporter headed to Utoya was turned away by police before reaching the lake that surrounds the island, as eight ambulances with sirens blaring entered the area. Police blocked off roads leading to the lake.
Emilie Bersaas, identified by Sky News television as one of the youths on the island, said she ran inside a school building and hid under a bed when the shooting started.
"At one point the shooting was very, very close (to) the building, I think actually it actually hit the building one time, and the people in the next room screamed very loud," she said.
"I laid under the bed for two hours and then the police smashed a window and came in," Bersaas said. "It seems kind of unreal, especially in Norway. This is not something that could happen here."
One of the youths at the camp, Niclas Tokerud, stayed in touch with his sister through the attack through text messages.
"He sent me a text saying 'there's been gunshots. I am scared (expletive). But I am hiding and safe. I love you,"' said Nadia Tokerud, a 25-year-old graphic designer in Hokksund, Norway.
As he boarded a boat from the island after the danger had passed he sent one more text: "I'm safe."
The United States, European Union, NATO and the U.K., all quickly condemned the bombing, which Britain's Foreign Secretary William Hague called "horrific" and NATO Secretary-General Anders Fogh Rasmussen deemed a "heinous act."
"It's a reminder that the entire international community has a stake in preventing this kind of terror from occurring," President Barack Obama said.
Obama extended his condolences to Norway's people and offered U.S. assistance with the investigation. He said he remembered how warmly Norwegians treated him in Oslo when he accepted the Nobel Peace Prize in 2009.
Nobel Peace Prize Chairman Thorbjorn Jagland said it appeared the camp attack "was intended to hurt young citizens who actively engage in our democratic and political society. But we must not be intimidated. We need to work for freedom and democracy every day."
Although police would not speculate on who was responsible for Friday's attack or whether international groups were involved, Norway has been grappling 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.
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.
Scandinavian countries have focused on anti-terrorism tactics that frustrate countries like the U.S. that are more aggressive about making arrests. Scandinavian authorities fight terrorism by disrupting plots, sometimes telling suspects they know what they're up to, and warning them of the consequences.
Terror convictions are also difficult to get because of skepticism in Scandinavian courts toward cases built on intent -- as most terrorism trials are -- and a demand for more evidence than in the U.S. and many other places.
Al Qaeda has promised attacks on Norway for years. The terror network's leader Ayman al-Zawahiri threatened the country in 2004 over its involvement in the U.S.-led military operation in Afghanistan and strategist Abu Yahya al-Libi made similar threats in 2006, the same year the Norwegian Embassy was attacked in Syria.
Norway's support of NATO's mission in Libya also earned it enemies, said Bob Ayers, a former U.S. intelligence officer.
"Norwegians are in Afghanistan. They're in Tripoli. They reprinted the cartoons," Ayers said.
Many intelligence analysts said they had never heard of Helpers of Global Jihad, which took initial credit. Ansar al-Islam also took credit on some jihadist web sites.
Whoever was responsibe, Ayers said it appeared more than one person was involved.
Asked at a press conference in Tripoli about Libya's reaction to the events in Oslo, government spokesman Moussa Ibrahim said, "We never support any acts of terrorism whatsoever."
But he suggested NATO's policies could have prompted the attack, saying, "NATO is planting terrorism in the hearts of many. This is unfortunate and sad."
Europe has been the target of numerous terror plots by Islamist militants. The deadliest was the 2004 Madrid train bombings, when shrapnel-filled bombs exploded, killing 191 people and wounding about 1,800. A year later, suicide bombers killed 52 rush-hour commuters in London aboard three subway trains and a bus. And in 2006, U.S. and British intelligence officials thwarted one of the largest plots yet -- a plan to explode nearly a dozen trans-Atlantic airliners.
In October, the U.S. State Department advised American citizens living or traveling in Europe to take more precautions following reports that terrorists may be plotting attacks on a European city. Some countries went on heightened alert after the May 2 killing of Osama bin Laden.
Intelligence analysts said they doubted the attack was linked to bin Laden's death.
"Al Qaeda would have targeted something closer to U.S. interests if it was related to bin Laden," Ayers said.