U.S. authorities have tightened the security at some airports in reaction to possible terror incidents in Britain on Friday and Saturday.

Despite the tightened security, there was no indication of any specific or credible threat to the United States, and there was no change in the overall security level, White House spokesman Tony Snow said in Kennebunkport, Maine, where President George W. Bush was meeting his Russian counterpart, Vladimir Putin, over the weekend.

The Transportation Security Administration had tighten security measures at some airport, and that would cause some inconvenience to passengers, he said.

Bush had been briefed about the ongoing developments in London, Snow said.

In a statement, Homeland Security Secretary Michael Chertoff said the government had no plans at this time to change the national threat level, but reminded the public "that the aviation threat level has been raised to orange since last fall."

As a precaution during the holiday period, Chertoff said, the Homeland Security Department would implement plans to increase security measures at airports, mass transit and other transportation facilities, he said.

"Some of these measures will be visible; others will not," he added.

Chertoff said U.S. authorities had been in close contact with their counterparts in Britain regarding the incidents at the Glasgow airport and the car bomb discoveries in London, but that there was not "no specific, credible information" at this point suggesting that latest incident was connected to a threat to the United States.