No one has yet claimed credit for a big apparent explosion near the Prime Minister's Office in Oslo, Norway.  ABC News cites "sources" that it was vehicle bomb. Drudge linked to the video below, indicating the extent of the damage.

Norway has not been on the front line of jihad, but last year an alleged Al Qaeda terror plot involving Norwegian residents was broken up by European authorities.  Of course, this could be something other than jihad-related, though I have been unable to find evidence of any domestic terrorism in Norway, other than this.  I doubt it was Svalbard separatists.

Update.  USA Today notes:

The AP also reports that a Norwegian prosecutor filed terror charges this week against an Iraqi-born cleric for threatening Norwegian politicians with death if he is deported from the country. The indictment centered on statements that Mullah Krekar - the founder of the Kurdish Islamist group Ansar al-Islam - made to various media, including the American network NBC.

 Update: The Guardian notes reports of a separate attack:

 Four people have been killed on the island of Utoya, an official from the AUF, the youth wing of the Labour party, told Varden (note that there are no other reports of deaths in Utoya at present, just that five people have been shot with no details of their condition).

Now it's complete panic and we swim off to get to safety.

County Secretary Telemark AUF says that there is panic on the summer camp of the Labour Party's Youth Camp.

There has been a shootout.

Are there any that are damaged?

Many people are shot.

Have you seen any dead?

Based on what I have seen, the innermost four people are shot and killed.

Other reports have the death toll in Oslo at 4.

Update: As of 4:17 PM EDT, acccording to USA Today, the death toll in Oslo is estimated at 7, and 9 or 10 at the youth camp