Airlines said flights were returning to normal on Friday but warned of more cancellations and further delays at UK airports after a foiled bomb plot sparked a security alert and stranded thousands of passengers.

Airport operator BAA said a ban on short-haul flights coming into Heathrow had been lifted and the airport was "busy but calm".

British Airways said about 70 percent of its short-haul services from Heathrow were expected to operate on Friday, a day after canceling all short-haul flights to and from the airport.

Most long-haul flights from Heathrow were operating as normal, except for six services to the United States, the airline said, but warned of delays at Heathrow and Gatwick airports.

"While the airline is hoping to operate a near-normal schedule, it is advising customers that they still could face delays at the airport and that the security restrictions introduced yesterday on all UK airports remain in place," BA said in a statement.

On Thursday, airlines banned hand luggage on flights out of the UK and warned of severe delays at London airports after British police said they had foiled a plot to blow up aircraft mid-flight between Britain and the United States.

British low-cost carrier easyJet said it had canceled about 80 flights on Friday compared with 300 a day earlier and said operations were returning to normal.

Dublin-based Ryanair listed about 30 cancellations from Stansted Airport on its web site. The airline canceled 120 flights on Thursday.

Virgin Atlantic said it expected to operate its normal flight schedule on Friday but warned of some delays. UK carrier bmi had also resumed its flights.

BAA, which operates Heathrow, Gatwick and Stansted airports, said it had been told the new security measures were in place indefinitely and it had deployed extra staff at airports to reduce delays.

A BAA spokesman said passengers were still allowed to take duty-free items bought after clearing customs and security onto flights, except for those to the United States.