CNN terrorism analyst Paul Cruickshank says the Oslo blast has all the hallmarks of a major attack, although the exact cause is not known.
It's too early to draw any conclusions on whether it was terrorism and who would carry it out, says Cruickshank. But, he said, by looking at the extent of the damage, it was plain to see the hallmarks of a major attack.
Cruickshank said that in recent months, there had been increased "chatter" about Norway, which had been investigating militants suspected of being linked to al Qaeda.
Norway also drew the ire of al Qaeda for publishing the controversial political cartoons of the Prophet Mohammed that originally appeared in a Danish newspaper and sparked outrage in the militant Islamic community.
The Scandinavian country also plays a part in NATO's operation in Afghanistan, and now, in Libya.
Norway has been largely spared from terrorism. But last December, an attempted suicide bombing in Stockholm shocked neighboring Sweden.
In July of last year, Norwegian authorities announced the arrests of three suspects in connection with an investigation into terrorist plots in New York and the United Kingdom.
The three were suspected of plotting terrorist attacks and having connections to al Qaeda, the prime minister's office said at the time.