British Prime Minister Tony Blair is calling this morning's attacks on London's subway system "barbaric" and vowed that "terrorism would not succeed." Three blasts tore through London's subway system during morning rush hour. Another blast ripped the top off a double-decker bus. The explosions all occurred during a one-hour interval. According to the Associated Press, two U.S. law enforcement officials said at least 40 people were killed in the attacks. Blair, who was attending the G-8 summit in Scotland, left the event to return to London. In a statement, he said it was important "that those engaged in terrorism realize that our determination to defend our values and our way of life is greater than their determination to cause death and destruction to innocent people." A group calling itself "The Secret Organization of al-Qaida in Europe" claimed responsibility for the attack. Across Europe and in the United States, transit systems are taking extra precautions against possible terrorist attacks.