The White House has condemned the attack targeting a convoy carrying former Pakistani Prime Minister Benazir Bhutto.
U.S. National Security Council spokesman, Gordon Johndroe, said Thursday the United States mourns "the loss of innocent life" in Karachi.
The NSC spokesman added, "Extremists will not be allowed to stop Pakistanis from selecting their representatives through an open and democratic process."
In New York, U.N. Secretary-General Ban Ki-moon expressed shock by news of the attack and extended condolences to the families of the victims.
The European Union also denounced the deadly bomb blasts, while Pakistani President Pervez Musharraf called the attacks "a conspiracy against democracy."
Speaking from Dubai, Ms. Bhutto's husband, Asif Ali Zardari, alleged that a Pakistani intelligence agency was behind the bloodshed.
Some information for this report was provided by AFP, AP and Reuters.