This morning we were greeted with the news of a massive car bombing at a government building in Oslo, Norway. We don't know who was behind the bombing, but Norway's intelligence agency said in February that Islamic extremism was a major threat to the country. Now officials report that a group called 'Helpers of Global Jihad' claims responsibility for the Oslo attack:

NORWAY police urged residents of Oslo today to avoid big gatherings and stay home after a powerful bomb rocked government and media buildings in the capital, causing deaths and injuries.

Police said a bomb caused the explosion, and Norwegian media reported that at least two people had died and several were injured.

In a separate incident, a man disguised as a police officer opened fire at a youth meeting of the ruling Labour Party in Utoeya, an island on the outskirts of the capital Oslo, state television NRK reported.

Prime Minister Jens Stoltenberg had at one point been scheduled to attend the event, police said.

[...] The death toll was believed to be two people, but authorities feared it would rise.

Police said a bomb was behind the explosion and Norwegian media reported that at least two people died.

[...] Islamic extremism is "our main priority and our main concern," PST chief Janne Kristiansen said at the time, while presenting the agency's annual risk assessment report.

The report said: "Although few people in Norway support Islamic extremism, there are activities within some groups that could contribute to heightening the security risk in 2011." NATO member Norway, which counts some 500 troops in Afghanistan, has never suffered an attack at home by Islamic extremists.

However, police last year arrested three Muslim men based in Norway suspected of planning an attack using explosives in the Scandinavian country. Norwegian prosecutors earlier this month also filed a terrorism charge against Mullah Krekar, founder of the Kurdish Islamist group Ansar al-Islam, who was accused of threatening a politician with death over his potential deportation from the country.

Krekar had warned that "Norway will pay a heavy price" if he were deported.

Norwegian F-16 fighter jets are also participating in air strikes in Libya, though the country has said it will withdraw its forces from the Libya operations on August 1.

The Norwegian military said in May that it had been the victim of a serious cyber attack at the end of March on the day after its jets for the first time carried out bombings in Libya.