Flanked by fellow world leaders, British Prime Minister Tony Blair said deadly explosions in London would not halt the work of their annual summit.
"We will not allow violence to change our societies or our values nor will we allow it to stop the work of this summit," Blair said in a statement on behalf of the Group of Eight leaders and the heads of other nations meeting in Gleneagles. "We will continue our deliberations in the interest of a better world."
Earlier, Blair termed the blasts terrorist attacks and said it was reasonably clear they were "designed and aimed to coincide" with the meeting.
"We are united in our resolve to confront and defeat this terrorism that is not an attack on one nation but on all nations and on civilised people everywhere," the world leaders said in a statement.
After reading the statement, Blair was leaving the summit for the day to return to London. President Bush conferred in a secure video-conference with national security and homeland security officials in Washington.
The leaders-- already protected by extraordinary security measures that local authorities said were sufficient for now-- planned to proceed with discussions on the issues of global warming and African poverty that Blair has made the centrepiece of the gathering.
"All of our countries have suffered from the impact of terrorism," the leaders said. "Those responsible have no respect for human life."
At least six blasts rocked the London subway and tore open at least one packed double-decker bus in nearly simultaneous explosions during Thursday's morning rush hour. Deaths and injuries mounted and officials shut down the entire underground transport network.
The explosions came as Bush and Blair were meeting over breakfast and answering questions from reporters.
"It's particularly barbaric that this has happened on a day when people are meeting to try to help the problems of poverty in Africa, the long-term problems of climate change and the environment," Blair told reporters.
G-8 leaders took a long break in their morning opening session so they could get individual briefings on developments.
"Today's bombings will not weaken in any way our resolve to uphold the most deeply held principles of our societies and to defeat those who would impose their fanaticism and extremism on all of us," the world leaders said in the statement read by Blair. "We shall prevail, and they shall not."
Liz Kirkham, spokeswoman for Tayside Police Force, which covers the Gleneagles area, said no additional security precautions were being taken at the summit as a result of the blasts, as substantial measures had already been put in place.
There was no immediate word on who was responsible.
"Just as it is reasonably clear that this is a terrorist attack or a series of terrorist attacks, it's also reasonably clear that it is designed and aimed to coincide with the opening of the G-8," Blair said.