Suspected British suicide bombers were just days away from simultaneous attacks on transatlantic airliners when officials said they foiled what one senior police commander called "mass murder on an unimaginable scale."

British police arrested 24 people over a plot to smuggle bombs on to aircraft disguised as drinks, and new tough security measures for air travel remained in place on Friday. Airports were jammed on Thursday and scores of flights were canceled.

Airline passengers wait in a security line as drinks are thrown away in a trash can outside of security at San Jose International Airport in San Jose, Calif., Thursday, Aug. 10, 2006. The United States issued its highest terrorism alert for commercial flights from Britain and raised security for all air travel Thursday after a major terror plot was foiled in London. [AP]

"(The bombers) were a couple of days from a test, and a few days from doing it," said a U.S. intelligence official, declining to be named.

"The plan was to have multiple suicide bombings on aircraft, essentially at the same time," said U.S. Homeland Security Secretary Michael Chertoff, adding al Qaeda might have been involved but that it was too early to draw conclusions.

US President Bush said the plan was a stark reminder his country was at "war with Islamic fascists."

The suspected plot raised the specter of strikes to rival the September 11, 2001 attacks on the United States that killed about 3,000 people and came 13 months after four British Muslim suicide bombers killed 52 people on London's transport network.

U.S. officials said as many as 10 planes might have been struck. Transatlantic jumbo jet flights usually carry more than 300 people, suggesting a death toll in the thousands.

"We are confident we have disrupted a plan by terrorists to cause untold death and destruction," said the London police force's Deputy Commissioner Paul Stephenson. "Put simply, this was intended to be mass murder on an unimaginable scale."