But he warned in his weekly radio address that the American people "must never make the mistake of thinking the danger of terrorism has passed."

The foiled plot in Britain to blow up passenger flights bound for the United States and the arrests of over 20 suspects this week reminded people of "a hard fact: the terrorists have to succeed only once to achieve their goal of mass murder, while we have to succeed every time to stop them," he said.

The plot appeared to have been carefully planned and well-advanced, and was further evidence that terrorists were "sophisticated, and constantly changing their tactics," said the president.

Bush said the arrests had significantly disrupted the threat, but one "cannot be sure that the threat has been eliminated."

"We're dealing with a new enemy that uses new means of attack and new methods to communicate," he said.

As terrorists had planned to use liquid explosives to blow up planes in mid-air, authorities adjusted security precautions by temporarily banning most liquids as carry-on items on planes, he said.

He urged people to show patience, cooperation and vigilance when traveling by air, as "the inconveniences you will face are for your protection."