U S heightens air security after bomb plot foiled

WASHINGTON, Aug 10 (Reuters) The US government heightened security on passenger planes and barred air travelers from carrying liquids today after Britain said it foiled a plot to blow up flights to the United States.

US officials said the aim was to blow up the planes in flight. One official said there were no signs the attacks were directed at any one city, but they might have taken place on flights heading to major US cities.

Homeland Security Secretary Michael Chertoff said al Qaeda might have been involved.

''This operation is in some respects suggestive of an al Qaeda plot, but because the investigation is still under way, we cannot yet form a definitive conclusion. We're going to wait until all the facts are in,'' he told a news conference.

The Department of Homeland Security said it took the unprecedented step of raising the threat level for commercial flights originating in the United Kingdom to ''severe'' or red, its highest level.

The threat level for all other commercial aircraft operating in or destined for the United States would be raised to ''high,'' or orange, Chertoff said.

Britain said the plot may have involved a ''liquid chemical'' device, and US Homeland Security barred passengers from carrying liquids, including beverages, hair gels and lotions, aboard planes.

The White House said the foiled plot was a ''direct threat'' to the United States. ''This was a serious threat to our country and the UK,'' White House spokesman Tony Snow said in a statement.

Snow said President George W Bush had talked twice on the telephone with British Prime Minister Tony Blair about the plot -- on Sunday and yesterday.

Bush was to make a statement on the plot when he arrived on a visit to Green Bay, Wisconsin, at about 2120 hrs, Snow told reporters traveling with the president.

Chertoff said the United States was sending air marshals to Britain to help increase security on flights to the United States.

FBI Director Robert Mueller said there was no evidence any of the plotting took place within the United States, which was one of the centers for the planning, preparation and execution of the Sept. 11 hijacked plane attacks on New York and Washington that killed almost 3,000 people.

Snow said Bush had been kept fully briefed on the plot, ''especially as the actions by the British became more imminent.'' Snow would not discuss any of the operational details of the investigation or the timing of the arrests in Britain, but said: ''There were some signs they (the British) thought it was time to move.'' Canada also said it had increased airport security in coordination with the United States and Britain, banning passengers from bringing gels and liquids on all flights and stepping up screening.

Chertoff told the news conference the plot was in the final planning stages. He said he considered US air travel safe following the precautions taken on both sides of the Atlantic.

A US official who asked not to be further identified said United Airlines, Continental Airlines and American Airlines flights between Britain and the United States had been specifically targeted for attack.

REUTERS MQA KP2251