OSLO, Norway — A police operation is under way in Oslo on Sunday and an official said it was related to a bombing on government headquarters. The explosion was followed by a shooting spree, and the twin attacks have shaken the peaceful nation.

Survivors of the massacre have said there were two assailants, and police were looking for a second suspect. One man has already been charged.

Police spokesman Anders Fridenberg said that the operation was eastern Oslo, but he would not give any further details. The neighbourhood appeared to be residential.

On Friday, a bomb rocked central Oslo, killing seven people. Hours later, gunman opened fire on a nearby island that was hosting a retreat for members of the left leaning Labor Party's youth wing. At least 85 people died there.

The man blamed for the attacks said he was motivated by a desire to bring about a revolution in Norwegian society, his lawyer said Sunday.

A manifesto published online -- which police are poring over and said was posted the day of the attack -- ranted that the European elite, "multiculturalists" and "enablers of Islamization" would be punished for their "treasonous acts." Police have not confirmed that their suspect, 32-year-old Anders Behring Breivik, wrote the document, but his lawyer referred to it and said Breivik had been working on it for years.

Police and his lawyer have said that Breivik confessed to the twin attacks, but denied criminal responsibility for a day that was the deadliest ever in peacetime. He has been charged with terrorism and will be arraigned on Monday.

In all, 92 people were killed and 97 wounded. There are still people missing at both scenes, and divers searched the waters around the island Saturday for bodies. Body parts remain inside the Oslo building, which housed the prime minister's office.

Norway's King Harald V and his wife Queen Sonja and Prime Minister Jens Stoltenberg joined mourners on Sunday at Oslo Cathedral, where the pews were packed, and the crowd spilled into the plaza outside the building. The area was strewn with flowers and candles, and people who could not fit in the grand church huddled under umbrellas in the rain.