Pakistani President Pervez Musharraf has offered his condolences to George W Bush over the death of an American diplomat in the blast in Karachi on Thursday.
Terming it as a "senseless act", he said that this would not deter their resolve to fight against "the evil of terrorism."
"We condemn this outrage in the strongest terms. Our authorities are investigating the incident. Those responsible will be brought to justice," he said in a message to Bush.
"This senseless act will not deter our strong resolve to pursue the relentless fight against the evil of terrorism," he added.
In a separate message to Bush, Pakistani Prime Minister Shaukat Aziz said that the attack was "aimed not only at the Pakistani nation but also at our friendly ties with the United States."
Five persons, including the diplomat and his Pakistani driver, were killed and dozens were wounded in the blast.