A statement released by the US Presidency said: "President Bush offered his sincere condolences to the families of all those lost in vicious attack." "The US strongly condemned the terrorist attack that took place in Islamabad, Pakistan. This is a reminder of the threat we all face. The US will stand with Pakistan's democratically elected government as they confront this challenge," the statement signed by national Security Council spokesman Gordon Johndroe said.
The US State Department said that it was in contact with the US embassy in Islamabad about the deadly blast and was looking into whether any US nationals were hurt.
On the US campaign trail, Democratic White House hopeful Barack Obama said the attack demonstrated the 'grave and urgent threat' that al-Qaeda and its affiliates posed to the US, to Pakistan, and to the security of all nations.
"As the attack earlier this week on our embassy in Yemen showed, over seven years after 9/11, the terrorist threat knows no borders, and the terrorists threatened innocent civilians of all religions and regions. Now is the time to refocus our efforts on defeating al-Qaeda and securing the American people," Obama said.
His Republican rival John McCain described the attack as an outrageous act of violence", which in his words, "must serve to deepen the resolve of Americans and Pakistanis alike to aggressively confront those terrorist groups that seek our destruction."
McCain added: "The attack also served 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."