Bush, who used his weekly radio address to announce the veto, said the program had helped stop plots against a Marine camp in Djibouti and the U.S. consulate in Karachi, Pakistan, and plans to fly passenger planes into a Los Angeles tower or London's Heathrow Airport and city buildings.

"Were it not for this program, our intelligence community believes that al-Qaeda and its allies would have succeeded in launching another attack against the American homeland," the president said.