British authorities said Thursday they had thwarted a terrorist plot to simultaneously blow up several aircraft heading to the U.S. using explosives smuggled in carry-on luggage. Heathrow was closed to most flights from Europe, and British Airways canceled all its flights Thursday between the airport and points in Britain, Europe and Libya.
Britain's Home Secretary John Reid said 21 people had been arrested in London, its suburbs and in Birmingham following a lengthy investigation, including the alleged "main players" in the plot.
Officials raised security to its highest level in Britain and banned carry-on luggage on all trans-Atlantic flights. Huge crowds formed at security barriers at London's Heathrow airport as officials searching for explosives barred nearly every form of liquid outside of baby formula.
The extreme measures at a major international aviation hub sent ripple effects throughout the world. Washington raised its threat alert to its highest level for commercial flights from Britain to the United States amid fears the plot had not been completely crushed. The alert for all flights coming or going from the United States was also raised slightly.
Two U.S. counterterrorism officials said the terrorists had targeted United Airlines, American Airlines and Continental Airlines. They spoke on condition of anonymity because of the sensitivity of the case.
A U.S. intelligence official said the plotters had hoped to target flights to major airports in New York, Washington and California, all major summer tourist destinations.
The suspects were "homegrown," though it was not immediately clear if they were all British citizens, said a police official who spoke on condition of anonymity because of the sensitivity of the case. Police were working closely with the South Asian community, the official said.
The official said the plotters intended to simultaneously target multiple planes bound for the United States.
"We think this was an extraordinarily serious plot and we are confident that we've prevented and attempt to committee mass murder on an unimaginable scale," Deputy Commissioner Paul Stephenson said.
London's Heathrow airport was the departure point for a devastating terrorist attack on a Pan Am airplane on Dec. 21, 1988. The blast over Lockerbie, Scotland, killed all 259 people aboard Pan Am Flight 103 and 11 people on the ground.
The explosive was hidden in a portable radio which was hidden in checked baggage.