Airports across the United States beefed up security Thursday and the White House said the foiled terror plot targeting flights from Britain to the United States poses "a serious a threat to our country and the UK."

"We do believe the plot involved flights from the UK to the U.S. and was a direct threat to the United States," said White House press secretary Tony Snow in Texas, where U.S. President George W. Bush is taking a 10-day vocation.

Snow said Bush has been briefed on the situation from his aides while at his ranch in Crawford, Texas, and is in close contact with British Prime Minister Tony Blair on the issue.

The spokesman praised U.S. and UK anti-terror officials for co-thwarting the plot which involves explosives smuggled on board flights in hand luggage.

"This is an ongoing investigation that will play out over several days and weeks," Snow said, adding the Bush administration will constantly evaluate the nature of the threat and adjust measures.

According to schedule, Bush will address the issue during a visit to Green Bay, Wisconsin later Thursday.

Earlier in the day, the administration raised the threat level for flights from Britain to "red," designating a severe risk of terrorist attacks. It is the first time the red alert level in the Homeland Security warning system has been invoked.

All other flights, including all domestic flights in the United States, were put under an "orange," alert-one step below the highest level.

The administration also banned all liquids and gels from flights, including toothpaste, makeup, suntan lotion, but baby formula and medicines were exempted.

Airports across the United States beefed up security Thursday and some flights were canceled or delayed in the wake of a foiled terror plot targeting airlines traveling from Britain.

Source: Xinhua