Western governments lined up to condemn Friday's twin attacks in Norway, saying the ‘cowardly’ perpetrators who killed at least 11 people had demonstrated a complete lack of humanity.

With Norway involved in both the Afghan and Libya campaigns, NATO's chief said the alliance stood united against the ‘heinous’ acts of violence.

The US government meanwhile said that President Barack Obama had been briefed about the attacks by John Brennan, his top adviser on counter-terrorism, which Washington described as ‘despicable.’

"On behalf of NATO, I condemn in the strongest possible terms the heinous acts of violence in Norway," said Secretary General Anders Fogh Rasmussen.

"Our solidarity with Norway remains steadfast. NATO countries stand united in the battle against these acts of violence."

Norwegian combat jets have conducted bombings in the air war against Muammar Gaddafi's regime in Libya, but the country is withdrawing the warplanes at the end of the month.

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.

Norway also has around 500 military personnel in Afghanistan, primarily in Kabul and in the north.

Rasmussen's words were echoed by Herman Van Rompuy, the president of the European Union, who spoke of his ‘deep shock’ at the killings.

"I condemn in the strongest terms these acts of cowardice for which there is no justification."

Van Rompuy said he sent a message of ‘condolences and solidarity’ from the 27-nation EU to Prime Minister Jens Stoltenberg.

European parliament president Jerzy Buzek expressed his solidarity with the Norwegian people over the ‘regrettable and despicable’ acts.

"Norway has been providing good services for peace in the most volatile spots areas around the globe," he said.

"The last thing Norway deserves is a terrorist attack on its soil. Terrorist attacks are never justified anywhere."

British Foreign Secretary William Hague also offered his condolences to all those bereaved or injured as a result of a ‘horrific’ bomb attack in Oslo, saying he condemned all forms of terrorism.

"I send my deepest condolences to all those who have lost relatives or been injured," Hague said in a statement.

"The UK stands shoulder to shoulder with Norway and all our international allies in the face of such atrocities. We are committed to work tirelessly with them to combat the threat from terrorism in all its forms."

French President Nicolas Sarkozy condemned what he said was an ‘odious and unacceptable act’ of violence.

Dutch Prime Minister Mark Rutte said that the attackers had shown a total lack of respect for human life.

"My thoughts are with the victims and their loved ones. Prime Minister Stoltenberg, the Norwegian government and the Norwegian people have my full my full support to use all force necessary to deal with this dreadful event," he said.

There was similar condemnation from the United States.

"We condemn these despicable acts of violence," State Department spokeswoman Heide Bronke Fulton said.

"Our hearts are with the victims and their families, and we have reached out to the Norwegian government to express our condolences."

Fulton said that the embassy in Oslo has urged all US citizens to avoid central Oslo and to "remain vigilant and aware of surroundings". She said that the United States was not aware of any casualties or injuries to US citizens.

"The US has reached out to the Norwegian authorities to offer assistance, but there have been no specific requests from the Norwegians thus far," Fulton said.