Terrorist attack on Oslo?

A surrealistic scene for Norway, smoke coming out of the government building, Oslo center is covered by smoke. The heart of the nation´s political power was attacked by a major blast at 15.30 Friday afternoon July 22. Almost all windows at the "Y block" and surrounding buildings was crushed. This devastating attack resulted in big damages and casualties are reported. It´s too early to say exactly what caused the explosion. Is this a counter attack towards Norway from Libya , Afghanistan or from others who regard Norway as an enemy?