The president also extended his condolences to Norway's people.
Addressing reporters after an Oval Office meeting with New Zealand's prime minister, Obama said he remembered how warmly Norwegians treated him when he traveled to Oslo to accept the Nobel Peace Prize in 2009.
He said "our hearts" go out to the Norwegian people. He also offered U.S. assistance with the investigation.
"It's a reminder that the entire international community has a stake in preventing this kind of terror from occurring," Obama said.
Norwegian authorities say the blast ripped open buildings, including the prime minister's office, and was followed by a shooting at a youth camp.
It was the peaceful nation's worst violence since World War II.
Norwegian Prime Minister Jens Stoltenberg was working at home at the time.
Later Friday, a man dressed as a police officer opened fire at a youth camp near the capital. Police had a suspect in custody in the shootings and say they believe the incidents are linked.
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