Western powers condemned the "disgraceful" attack on Saturday on an Islamabad hotel that killed at least 60 people, voicing their resolve to support Pakistan in the fight against violent extremism.
Swift condemnation came from Washington, where the White House said the attack in Pakistan was yet another wake-up call about the global threat from extremism.
"This is a reminder of the threat we all face," said national security council spokesman Gordon Johndroe in a statement.
"The United States will stand with Pakistan's democratically elected government as they confront this challenge," he added.
British Foreign Secretary David Miliband said: "This latest bombing attack in Islamabad is yet another shocking and disgraceful attack without justification."
It should be deplored by the entire international community, he added.
Britain stood "shoulder-to-shoulder with the government of Pakistan against the violent extremists who have no answers but only offer death and mayhem," said Miliband.
Police in Pakistan said that a suicide bomber detonated a truck packed with explosives, killing at least 60 people and injuring some 200 others, at the Marriott Hotel in Islamabad.
The attack came just hours after the country's new president, Asif Ali Zardari, delivered his first address to parliament, only a few hundred metres (yards) away.
After the attack, Zardari vowed that the country would "continue to fight terrorism and extremism in all its forms and manifestations and such dastardly acts cannot dent the government's commitment to fight this menace."
The president is due to meet US President George W. Bush in New York next week.
The European Union joined in expressing support for Pakistan which has long grappled with extremism from Al-Qaeda and Taliban militants, especially in the tribal areas along the border with Afghanistan.
"At this difficult time, the Presidency of the Council of the European Union addresses a message of solidarity to the Pakistani authorities, and stands more than ever with them in their fight against terrorism," the presidency, currently held by France, said in a statement from Brussels.
Spain and Italy also issued statements.
Spanish Prime Minister Jose Luis Rodriguez Zapatero extended his "deepest condolences to the families of the victims of this bloody attack", said a foreign ministry statement.
He expressed his solidarity "in these difficult moments" with the Pakistani people and their government, it added.
Italian Foreign Minister Franco Frattini "firmly condemned" the attack.
It underlined the need to "reinforce international collaboration, in particular with the countries of the region," to "wipe out terrorism," he said in his statement.
Democratic White House hopeful Barack Obama said the attack "demonstrates the grave and urgent threat that Al-Qaeda and its affilliates pose to the United States, to Pakistan, and to the security of all nations.
"As the attack earlier this week on our embassy in Yemen shows, over seven years after 9/11, the terrorist threat knows no borders, and the terrorists threaten innocent civilians of all religions and regions," Obama said.
His Republican rival John McCain described the attack as an outrageous act of violence" that "must serve to deepen the resolve of Americans and Pakistanis alike to aggressively confront those terrorist groups that seek our destruction."
The attack "also serves as one more demonstration of the need for the next president to work closely with our partners and allies in order to counter the dangers posed by radical Islamic extremism," he said.