LONDON — A massive bomb in downtown Oslo, Norway, and a horrific shooting rampage at a summer youth camp stunned the nation, killing at least 87 people in apparently related terrorist attacks in a nation long known as the home of the Nobel Peace Prize.
It was not immediately clear who was responsible for the attacks, but speculation swirled around both Islamic militant groups and domestic right-wing extremists.
Al-Qaida previously has singled out Norway as an intended target, and a shadowy group affiliated with the terrorist network reportedly claimed responsibility, a statement that could not be verified.
A suspect was arrested in the shooting, and reports described him as a tall, fair-haired man who spoke fluent Norwegian. The justice minister identified him as a Norwegian citizen.
Friday's double attacks, which police said were linked, recalled the 2008 siege on multiple sites in Mumbai, India, that raised international fear of coordinated, sophisticated attacks on "soft" targets unprepared for a large-scale assault.
The rampage on Utoya, a small, heavily wooded island not far from Oslo, was a particularly harsh blow. A youth convention of the ruling Labor Party, the biggest political event of the summer, was under way there. Hundreds of young people, some of them teenagers, were in attendance.
Authorities said at least 80 people were killed by a gunman whom witnesses described as a man dressed in a police uniform.
The suspect, a 32-year-old Norwegian, was arrested on Utoya. Police later found undetonated explosives on the island.
The prime minister's office was heavily damaged by the bomb blast in Oslo, which killed seven people. Norwegian news reports said that Prime Minister Jens Stoltenberg was working at another location and was unharmed. In a nationally televised address, he urged his compatriots not to be overcome by fear.
But the shock and scars from the violence will probably run deep in the normally placid, close-knit Scandinavian nation of about 5 million people. Authorities closed Norway's borders shortly after the attacks.
"Norway will stand together in a time of crisis," Stoltenberg said.
Addressing the attackers, he said: "You will not destroy our democracy and our ideals for a better world.... No one will bomb us into silence; no one will shoot us into silence."
At the White House, President Barack Obama sent his condolences to the Norwegian capital and called for stronger global cooperation to combat terrorism.
"It's a reminder that the entire international community has a stake in preventing this kind of terror from occurring," said Obama, who was awarded the Nobel Peace Prize in 2009. "We'll provide any support we can to them as they investigate these occurrences."
Mattias Carlsson, a Swedish journalist at Utoya, said he saw as many as 15 to 20 bodies on the shore and in the frigid waters around the island.
"Some have blood on their faces. There is clothing lying around at the shore, as if someone has tried to swim away," Carlsson said in a telephone interview. "There are four people and they are lying together as if they are hugging."
The shooting spree occurred not long after a bomb exploded in mid-afternoon in the center of Oslo. The location was near the prime minister's office and other government buildings, including the finance and oil ministries and the Supreme Court.
The blast, suspected to be a car bomb, was so powerful that it could be heard miles away, and blew out almost all the windows of an office tower. Seven people were killed and about 10 were injured, the justice minister, Knut Storberget, said.
Norwegian news reports said the man arrested on Utoya was also placed by witnesses at the scene of the bomb blast. There have been no reports so far of other plotters or attackers.
The SITE Intelligence Group, an independent organization that monitors Islamic extremist websites, said that a "prominent jihadist" named Abu Suleiman al Nasser claimed responsibility for the attack in a statement released on the Shumukh al Islam forum, which is linked to al-Qaida.
Nasser linked the assault to Norway's deployment of troops in Afghanistan and to a bombing and suicide attack in central Stockholm in December in which only the bomber died.
The statement demanded that European countries withdraw their forces from Afghanistan and warned: "What you are seeing is merely the beginning, and what is coming is more."
A few years earlier, Muslims worldwide were enraged by a Norwegian newspaper's publication of cartoons depicting the prophet Muhammad, which originated in Denmark. In 2006, protesters, who found the depictions blasphemous, set fire to the Norwegian Embassy in Damascus, the Syrian capital.
But Norwegian authorities said they were not jumping to conclusions about who was responsible.
Until Friday, the country's official threat assessment was at the lowest possible level, and has been for years, except for a few months several years ago when it was raised to moderate, said Siv Alsen, a spokeswoman for Norway's intelligence agency, the Norwegian Police Security Service.
The threat was considered low despite the arrests almost exactly a year ago of three men suspected of being affiliated with al-Qaida and plotting a terrorist attack. Two of the suspects were foreign-born legal residents of Norway, and the third was a foreign-born Norwegian citizen.
Last week, Mullah Krekar, an Iraqi-born cleric who lives in Norway, was charged with terrorism after allegedly threatening politicians with death if he is deported. Krekar is the founder of the militant Kurdish group Ansar al Islam.
And in 2003, an audio message from Ayman Zawahiri, who this year succeeded Osama bin Laden as leader of al-Qaeda, urged militants to attack the United States, Britain, Australia and Norway. Norwegians were puzzled by the inclusion of their country on the list; explanations centered on Norway's participation in the war in Afghanistan.
The country also faces a small but growing threat from neo-Nazi groups. There are indications that far-right extremists have established contact with organized criminal groups, which could give them easier access to weapons, the threat assessment said.
The bomb Friday left the streets of downtown Oslo carpeted with glass, documents, masonry and other debris. News agencies said the twisted, charred wreckage of a car could be seen close to the blast site.
"My first thought was that we were hit by lightning. So I ran onto the rooftop just to see if we had any damage," said Torbjorn Pedersen, a reporter at the newspaper Aftenposten. "But then I saw the smoke drifting from the (prime) minister's building."
The toll probably would have been far worse if not for the fact that many Norwegians are on their summer vacations and those still at work often leave early.
Not long after the blast, the shooting rampage began on Utoya. News reports said the gunman, wearing a police uniform, beckoned bystanders over to him, on the pretense that he wanted to speak to them about security measures in the wake of the bombing in Oslo. He then opened fire.
Emilie Bersaas, 19, told Sky News that she heard shooting, saw people running and screaming, then ran herself to a building to take cover. She and a friend piled clothes and a mattress onto a desk and hid under it.
"I felt kind of safe, but you never know," Bersaas said. "It's a lot of people on a small island. They're all shaken up right now."
(Chu writes for the Los Angeles Times. Times staff writers Ken Dilanian in Washington, Janet Stobart in London and special correspondent Alexandra Sandels in Beirut contributed to this report.)