People help a blast victim in Oslo
Western governments lined up to condemn twin attacks in Norway which have claimed at least 87 lives, slamming the "cowardly" perpetrators as they vowed to step up intelligence cooperation, reports AFP.
With Norway involved in both the Afghan and Libya campaigns, NATO's chief said the alliance stood united against the "heinous" acts of violence while US President Barack Obama urged countries around the world to step up cooperation in anti-terrorism efforts.
The attacks were "a reminder that the entire international community has a stake in preventing this kind of terror from occurring," Obama said during a meeting with New Zealand's Prime Minister John Key.
"We have to work cooperatively together on intelligence and in terms of prevention of these kinds of horrible attacks," added Obama.
UN Secretary-General Ban Ki-moon expressed shock and condemned the violence while extending his condolences.
"The United Nations stands together with the people of Norway at this terrible moment," said the UN chief's spokesman, Martin Nesirky.
NATO's Secretary General Anders Fogh Rasmussen said the alliance was united in its repugnance at the "heinous acts of violence in Norway".
"Our solidarity with Norway remains steadfast. NATO countries stand united in the battle against these acts of violence," he added.
Norwegian combat jets have conducted bombings in the air war against Moamer Gaddafi's regime in Libya, although it 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.
The condemnations from Rasmussen and Obama 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."
European Commission President, Jose Manuel Barroso voiced shock at the "abhorrent images" of the bomb blast in Oslo's government quarter.
Carl Bildt, Foreign Minister of neighbouring Sweden, expressed solidarity with his fellow Scandinavians.
"Terror has struck. We are all Norwegians," he said in a message on Twitter.
British Prime Minister, David Cameron said he was outraged by the "evil" attacks and pledged to work with Oslo to track down the perpetrators.
French President, Nicolas Sarkozy condemned what he said was an "odious and unacceptable act" of violence while Dutch Prime Minister Mark Rutte said that the attackers had "shown a total lack of respect for human life".
And in Berlin, German Chancellor Angela Merkel said she was "horrified". Her "government and the German people are standing by" Norway, she added.
"Canada condemns these barbarous and senseless acts of violence," Prime Minister Stephen Harper said as his Australian counterpart Julia Gillard also voiced outrage.