LONDON -Three British Muslims were convicted Monday of plotting to murder thousands by downing at least seven trans-Atlantic airliners in simultaneous attacks designed by al-Qaida to be the deadliest terrorist strike since Sept. 11, 2001.

Abdulla Ahmed Ali, 28, Assad Sarwar, 29, and Tanvir Hussain, 28 were found guilty at Woolwich Crown Court in London of leading a plan to detonate bombs on aircraft bound for the United States and Canada, using liquid explosives hidden in soda bottles.

Four other men were acquitted of conspiring to bomb airliners, but admitted lesser charges - and in one case conspiracy to murder. An eighth man was cleared completely.

The case brought sweeping new restrictions for air passengers, including limits on the amount of liquids and gels they can take carry on board.

British and US security officials said the plan was directly linked to al-Qaida and guided by senior Islamic militants in Pakistan.

Authorities estimate that, if successful, about 2,000 passengers would have died. Had the bombs been detonated over US and Canadian cities, hundreds more would have been killed on the ground. Britain's Home Secretary Alan Johnson said the plot would have brought "murder and mayhem on an unimaginable scale."

Other officials said the political repercussions would have been immense - likely destroying relations between London and Washington. The case may spur new concerns over the US visa waiver program, which allows citizens of many European Union countries - including Britain- to fly to the United States without visas.

Police officials said they believe the plotters were just days away from mounting their attacks when officers rounded up 25 people in 2006. The arrests led to travel chaos as hundreds of jetliners were grounded across Europe.

Prosecutors said the suspects had identified as targets seven flights from London's Heathrow airport to New York, Washington, San Francisco, Toronto, Montreal and two to Chicago.

Former US Deputy Secretary of State John Negroponte told the Senate in 2007 the plot "would have been on a par, or something similar to 9/11."

The plotters planned to assemble bombs in airplane toilets using hydrogen peroxide-based explosives injected into soda bottles, prosecutors said.

Britain's MI5 spy agency believes the group planned to strike as many as 18 jetliners in two waves of bombings, and to provoke further panic with attacks on U.K. power stations. Police say some would-be second-wave suicide bombers have likely evaded arrest.

Investigations into the secondary plots - and hopes of gathering evidence to link the cell to specific terrorists in Pakistan - were curtailed as US officials became increasingly nervous and ordered the arrest of one of the group's key accomplices in Pakistan.

Rashid Rauf, a British-born baker's son, is said by intelligence officials to have been the key link between the U.K. and militants in Pakistan. Rauf was arrested in the central Pakistani city of Bahawalpur in early August 2006.