British newspapers report that the leader of the al-Qaida terror network in Britain may be in custody after police last week broke up a plot to blow up passenger planes flying to the United States.
Authorities have not released the suspect's name.
Investigators have not yet made a direct connection between the plot and al-Qaida. But officials in Pakistan say one suspect arrested there for alleged involvement in the plot is believed to have ties to al-Qaida in Afghanistan.
British authorities have 23 suspects in custody. They allegedly planned to blow up as many as 10 airliners using liquid explosives. Police moved in after intercepting communications from a Pakistani suspect urging the British plotters to carry out the plot immediately.
British Home Secretary John Reid warned Sunday that other efforts to launch terror attacks in Britain are highly likely.
British airlines have imposed security measures severely restricting what can be carried on board planes, causing long delays. Officials at London's Heathrow Airport say they are canceling 20 percent of its flights Monday.
One third of all Heathrow flights were canceled Sunday.