Bush told reporters later that he had instructed authorities in the United States to be "extra vigilant" as people in the United States began going to work. The United States raised its terror alert to orange, or high, for the nation's mass-transit systems.
"The war on terror goes on," Bush said.
The President learned of the bombings from British Prime Minister Tony Blair during the opening session of the Group of Eight summit, an annual gathering for leaders from eight of the world's largest industrialized nations. Blair is host to this year's meeting at the Gleneagles golf resort. He rushed back to London after the blasts, then returned to the summit in the evening.
Officials traveling with Bush moved quickly to make sure that the relevant agencies in Washington were on alert for possible attacks on American targets. U.S. embassies around the world were warned to be extra vigilant.
After wrapping up the morning session at the G-8 summit, Bush retreated to his traveling command center in a suite that had been equipped in advance for just such an emergency. The facility, staffed by military communications experts, brought state-of-the-art technology to a Scottish resort that is so old-school, the guest activities include falconry.
The President got updates from Homeland Security Secretary Michael Chertoff, National Intelligence Director John Negroponte, and other top security advisers. McClellan said Bush planned to remain in Scotland until the summit concluded today. He was to be back in Washington by tonight.
Bush told reporters the resolve of other summit partners in combating terrorism "is as strong as my resolve. We will not yield to these people, will not yield to the terrorists."
The G-8 leaders pledged solidarity. German Chancellor Gerhard Schroeder called the bombings "perfidious attacks." Said French President Jacques Chirac: "This scorn for human life is something we must fight with ever greater firmness."
Canadian Prime Minister Paul Martin extended condolences to the victims. Russian President Vladimir V. Putin said through spokesman Alexei Gromov that "no matter where such inhuman crimes occur in London, New York, Moscow or other countries of the world - they demand unconditional condemnation."
Italian Prime Minister Silvio Berlusconi blamed "a band of fanatical criminals" for the attacks.
Liz Kirkham, spokeswoman for Tayside Police Force, which covers the Gleneagles area, said no additional security precautions were taken as a result of the blasts because substantial measures already had been put in place for the summit.
In a statement on behalf of all participants of the summit's business session - the United States, Britain, Japan, Germany, France, Italy, Canada and Russia, plus leaders of China, India, Mexico, Brazil and South Africa - Blair said the attacks were "not an attack on one nation but on all nations and on civilized people everywhere."
Contact reporter Ron Hutcheson at 202-383-6101 or firstname.lastname@example.org.
William Douglas of the Inquirer Washington Bureau contributed to this article, which also contains information from the Associated Press.