Ms Napolitano said today that major airports were seeing lines “150 to 200 per cent as long as we would normally expect” as result of the federal spending cuts that went into force on Friday.

“We’re already seeing the effects at some of the ports of entry, the big airports, for example. Some of them had very long lines this weekend,” she told a breakfast event organised by Politico.

When pressed for specifics she cited Chicago’s O’Hare, Atlanta’s Hartfield-Jackson and Los Angeles International Airport (LAX), adding: “I don’t mean to scare, I mean to inform.”

However, when contacted by The Daily Telegraph, spokespeople for both O’Hare and LAX, as well as representatives from the travel industry, denied that airports had been hit by delays.

“We haven’t had any slowdowns at all,” said Marshall Lowe, a spokesman for LAX. Mr Lowe said that he had been on duty over the weekend and received no reports of unusual security delays.

DeAllous Smith, a spokesman for Hartfield-Jackson, said: “There have been no abnormally long lines at the security checkpoint nor unusual aircraft delays at Hartsfield-Jackson Atlanta International Airport as a result of sequestration.”