At least seven people were killed in a pair of explosions apparently targeting Norway's government buildings in Oslo and at least 80 more killed in a shooting outside the capital, police said.
The tangled wreckage of a vehicle was seen near the Norwegian government building that was targeted in the blast, officials said. It was not clear if the car was a bomb vehicle or near the site of a blast. At least one explosion was the result of a massive vehicle bomb, U.S. government sources on the scene said.
Hours after the blasts, a gunman opened fire at a youth meeting on an island outside of Oslo, killing at least 80. One man was arrested in connection to both attacks. Norwegian Minister of Justice Knut Storberget said the man in custody was Norwegian but his motives are unclear at this time.
TV2, Norway's largest broadcaster, later identified the suspect as Anders Behring Breivik, 32, describing him as a member of "right-wing extremist groups in eastern Norway." Norwegian police would not confirm the identity of the suspect.
Norway's prime minister, Jens Stoltenberg, who has an office in a building hit by the blast, was uninjured and said in a statement the blast was "severe" and all available resources were being put into the rescue effort.
President Obama said the incident was "a reminder that the entire international community has a stake in preventing this kind of terror from occurring."
Pictures, posted on Twitter, show several buildings with windows blown out. Multiple tweets described people bleeding in the streets.
"It felt very big. It shook the whole building," Norwegian government official Anders Lande said of one explosion. "There was lots of glass. As I was evacuated, I saw several people injured."
U.S. ambassador to Norway, Barry White, said the United States "condemns these despicable acts of terrorism." The American ambassador said the attack will serve as a kind of wake-up call to Norwegians who may have thought they were safe from terrorism.
White said all US embassy staff were safe and accounted for.
ABC News' Matthew Mosk, Matthew Cole, Jim Sciutto, Martha Raddatz and Kirit Radia contributed to this report.