An injured woman is helped by a man at the scene of a powerful explosion that rocked central Oslo July 22, 2011. [Photo/Agencies]

OSLO - The deadly blast that shook Oslo city center on Friday and killed at least seven people was traced to explosives planted in a car, the Norwegian police said.

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They told a news conference held late Friday that the bomb was placed in a vehicle parked in front of a main government building. The bomb was detonated after the perpetrator had left the place.

The bomb went off just before 15:30 local time (13:30 GMT) Friday. Seven people were confirmed dead and some 16 others injured.