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.
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 Kadhafi'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."
Van Rompuy said he sent a message of "condolences and solidarity" from the 27-nation EU to Prime Minister Jens Stoltenberg.
European Commission president Jose Manuel Barroso voiced shock at the "abhorrent images" of the bomb blast in Oslo's government quarter.
"An attack of this magnitude is not something one would expect in Norway, famously associated with peace at home and peace-making abroad," Barroso said.
Carl Bildt, foreign minister of neighboring 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.
"These attacks are a stark reminder of the threat we all face from terrorism," he said. "I have offered Britain's help, including through our close intelligence cooperation.
"We will work with Norway to hunt the murderers who did this and prevent any more innocent deaths. We can overcome this evil, and we will."
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.
"A number of people have been killed and many more injured. Survivors have lived through a nightmare," she said.
New Zealand's prime minister John Key also voiced his "sympathies and concerns," adding: "If it is an act of global terrorism, then I think that what it shows is no country, large or small, is immune from that risk."