Airlines have warned the British government that the country's air travel is grinding to a halt because of tough new anti-terror security requirements.

British Airways and Ryanair on Saturday canceled scores of flights from Britain to Europe and the United States and blamed airport operator BAA for not investing enough in security systems and baggage screening in the aftermath of new terrorism threats.

Budget carrier Ryanair appealed to the British government to use police and army reservists to speed up searches at overloaded airport security checkpoints.

CountryWatch: United Kingdom

Heathrow Airport, the major hub for British Airways, canceled one-third of flights due out Saturday afternoon and night, blaming strict new security regulations. Passengers were delayed so long that many missed their flights.

Saturday night, the airport said it planned to cancel a third of its flights on Sunday, too, because of the current delays.

"To alleviate the stress on the operation, up to a third of the scheduled departing flights on Sunday 13 ... from Heathrow will be canceled," BAA said in a statement. "The remaining flights should depart from Heathrow on schedule or as close to schedule as possible."

Ryanair, which operates most of its London services through Stansted Airport, northeast of London, said it had complied with BAA orders to cancel more than 60 flights of its Stansted flights this weekend, about 20 percent of the total, but said this overloaded security situation must be fixed by Monday.

"Ryanair and other major UK airlines cannot keep canceling flights and disrupting the travel plans of tens of thousands of British passengers and visitors solely because the BAA cannot cope with the new body-search requirements," said Michael O'Leary, chief executive of Ryanair.

"If the British government is serious about defeating terrorism and not allowing the terrorists to disrupt normal, everyday British life, then it must provide the additional security staffing — either police or army reserve personnel — immediately to prevent London's main airports from grinding to a halt over the coming days," O'Leary said.

BAA PLC ordered the cancellations because its systems for screening passengers and checked-in baggage for security threats could not cope with the extra scrutiny required of passengers and their luggage in the wake of Thursday's thwarted threat to bomb up to 10 U.S.-bound aircraft.

"Whilst the need for this action is extremely regrettable, it is the only way that services at Heathrow can continue to return to normal operations," BAA, which owns both Heathrow and Stansted, said in a statement. It said cancellations would hit Heathrow departures from 1400 GMT to 2230 GMT.

British Airways said it canceled a quarter of its regional flights from Heathrow, including flights to Europe, Britain and the United States, and accused the airport owner of failing to cope with the problems posed by strict new security regulations.

"We are ready and able to operate a full schedule at London Heathrow. We have sufficient flying crew, ground staff and aircraft in place," said Willie Walsh, the airline's chief executive. "However BAA is unable to provide a robust security search process and baggage operation at London Heathrow, and as a result we are being forced to cancel flights and operate some others from Heathrow without all the passengers onboard."

Rainy, gusty weather added to the frustration of passengers who formed long lines waiting to be admitted to Heathrow's check-in area.