• Norwegian Prime Minister calls crisis meeting
• EU condemns 'cowardice' of Oslo bomb blast
• Obama sends condolences to Norway and urges global anti-terror cooperation
• Britain sends condolences over 'horrific' Oslo bomb
• NATO condemns 'heinous' attacks in Norway
• Police fear explosives at site of Norway shootings
• Four shot dead at Norway ruling party meeting
• Attacks in Scandinavian countries since 1999

OSLO, July 22, 2011 (AFP) - Militants staged twin bomb and shooting attacks in Norway Friday, leaving at least 11 dead as a blast tore through government buildings and a gunman opened fire at a youth meeting of the ruling party.

Many were also reported wounded from the bomb blast in central Oslo and the shooting at a summer school meeting of Prime Minister Jens Stoltenberg's ruling Labour Party outside the capital.

Authorities were reeling, with police saying they had no clue who or what was behind the attack, but media reported that the gunman behind the shooting had been arrested.

The United States and Europe immediately denounced the attacks and vowed solidarity with NATO member Norway -- an enthusiastic participant in international military missions that has forces in Afghanistan and is participating in Western air strikes in Libya.

Police said a "bomb" was behind a "powerful explosion" that tore through the government quarter in central Oslo, home to the prime minister's office, the finance ministry and some of the country's leading media.

Stoltenberg was safe and there were no reports of other senior government officials being killed or wounded. The government was to hold a crisis meeting later Friday.

"We can confirm that we have seven dead and two have been seriously injured" in the bomb attack, a police spokesman told reporters at a briefing in Oslo. Several dozen were also wounded, police said.

"We have no main theory, we don't even have a working theory," a police official said separately. "We already have enough to do to get an understanding of the situation."

Police did say however, that they believed the two attacks were connected.

"There are good reasons to believe that there is a link between the events," police commissioner Sveinung Sponheim told reporters in Oslo.

Media reports said a man disguised as a police officer opened fire on the youth meeting at a summer camp on Utoeya, an island just outside Oslo, where Stoltenberg had been scheduled to give a speech on Saturday to the 560 people attending.

Norwegian police said that there could be explosives on the island.

"From what I saw, at least four people have been shot and killed," Adrian Pracon, a participant at the event told the Varden newspaper.

NRK public television reported that police had arrested the gunman, but police had neither confirmed the arrest nor released any details on casualties.

Oslo's mayor Fabian Stang said the capital was struggling to come to terms with the idea that it had joined the list of cities targetted by bombers.

"Today we think about those people living in New York and London who have experienced this kind of thing," he told Britain's Sky News.

"I do not think it is possible for us to understand what has happened today but hopefully we will be able to go on and that tomorrow Oslo will be a peaceful city again."

Images on Norwegian television showed the prime minister's office and other buildings heavily damaged, sidewalks covered in broken glass and smoke rising from the area.

A police spokesman said a vehicle had been seen driving at high speed in the area just before the explosion but did confirm that the blast had been caused by a car bomb.

Police had sealed off the area, which also houses the country's biggest tabloid newspaper Verdens Gang (VG). They had also urged residents to stay in their homes.

Stoltenberg gave a telephone interview to show that he was unharmed after the deadly blast, which he called a "serious situation".

"Even if one is well prepared, it is always rather dramatic when something like this happens," he said in the interview with a Norwegian TV station.

The EU condemned the attacks as "acts of cowardice" and the NATO chief denounced the attacks as "heinous".

US President Barack Obama called the attacks "a reminder that the entire international community has a stake in preventing this kind of terror from occurring."

Witnesses said the damage around government headquarters was extensive while some said that police had spoken of two bombs.

"I see that some windows of the VG building and the government headquarters have been broken. Some people covered with blood are lying in the street," a journalist with public radio NRK said from the scene.

"There is glass everywhere. It is total chaos. The windows of all the surrounding buildings have been blown out," said NRK journalist Ingunn Andersen.

Norway's intelligence police agency (PST) said in February that Islamic extremism was a major threat to the country, describing Islamic extremism as "our main priority and our main concern".

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.

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 capital is also a well-known symbol of international peace efforts, home to the Nobel Peace Prize and the birthplace of the 1993 Israeli-Palestinian Oslo Accords.