The conspiracy is "a stark reminder that this nation is at war with Islamic fascists who will use any means to destroy those of us who love freedom, to hurt our nation," he said.
Mr Bush, who discussed the plot with British Prime Minister Tony Blair by teleconference on Sunday, praised London's "good work in busting this plot" and said US-British "cooperation on this venture was excellent."
"This country is safer than it was prior to 9/11. We've taken a lot of measures to protect the American people. But obviously we still aren't completely safe, because there are people that still plot and people who want to harm us for what we believe in," Mr Bush said.
"It is a mistake to believe there is no threat to the United States of America, and that is why we've given our officials the tools they need to protect our people," he said.
Alert level
US authorities issued their highest-level alert for the first time following revelations of the plot.
British police arrested 24 people allegedly involved in planning to bomb multiple US airliners over the Atlantic.
US officials estimate that up to 10 planes were targeted in the operation which they said bore the imprint of Osama bin Laden's Al-Qaeda network. Pakistani authorities said they had also made several arrests.
The plot prompted the US Homeland Security department to issue a code red threat warning covering US-bound planes from Britain.
It’s the first time the highest alert has been issued since the system was created following the September 11, 2001, Al-Qaeda attacks on New York and Washington.
"This had the earmarks of an Al-Qaeda plot," said Robert Mueller, head of the US Federal Bureau of Investigation.
"We have no indication at this point in time of plotting within the United States aligned at all or at all intersecting the plotters and the UK," Mr Mueller said.
"But that does not mean that there are not others around the world that have the same aspirations and would undertake the same type of plotting," he said.
US airlines targeted
US Homeland Security Secretary Michael Chertoff said the plot "had a lot of members, and it was international in scope".
He said the operation was to involve "multiple explosions in multiple aircraft", though he declined to provide further details.
But a US intelligence official said United Airlines, American Airlines and Continental Airlines were among the carriers targeted.
The destinations of the targeted flights included New York, Washington and Los Angeles, and possibly other major hubs such as Boston and Chicago, the officials said on condition of anonymity.
The governors of California and Massachusetts ordered the National Guard out to help boost security at airports in Boston and Los Angeles and extra measures were also put in place in New York.
But after some initial disruption and delays for passengers due to increased screening and baggage restrictions, most traffic quickly returned to normal at major airports, with the exception of some flights to and from London.
Mr Chertoff likened the plot to a foiled Al-Qaeda plan in 1995 to detonate bombs on 11 airliners flying to the United States over the Pacific.
He said the plotters had been very close to carrying out the attacks when British police moved in.
"They had accumulated and assembled the capabilities that they needed, and they were in the final stages of planning before execution," he said.
In addition to the red alert covering US-bound flights from Britain, the
Homeland Security department raised the threat level to "high," or orange, for all commercial aviation operating in or destined for the United States.
The advisory system consists of five levels: "low," or green; "guarded," or blue; "elevated," or yellow; "high," or orange; and "severe," or red.