The US administration's demands for armed guards on all flights from Europe to America, and for a new permit system, are the latest of increasingly strict measures introduced since 9/11.
After the 2001 attacks, when al-Qaida members hijacked four planes from within the US, the country's airport security was heavily criticised.
In February 2002, the Transportation Security Administration (TSA) assumed responsibility for airport security. Previously, it had been the responsibility of individual airlines, which employed private security firms.
Stricter security measures were introduced, such as electronic screening for every item of baggage passing through the country's 429 airports, and the number of passengers and bags being hand-searched was stepped up.
In 2004, the Department of Homeland Security introduced measures whereby foreign visitors had to be fingerprinted and photographed on arrival, allowing customs officials to check passengers instantly against terrorist watch lists and a national criminal database.
The foiled terrorist attack on US-bound flights from Heathrow airport in August 2006 pushed airport security back up the agenda. In October that year the EU agreed a deal making it easier for American intelligence agencies, including the FBI and the secret service, to access detailed personal information about transatlantic air passengers.
Under the agreement, US officials would be given conditional access to "passenger name record" information, which includes credit card details, full names and e-mail addresses. Washington had previously threatened to take away landing rights from European airlines that did not comply and to fine them thousands of pounds per passenger.
There is evidence that the increased security measures have had a negative impact on the numbers of foreign tourists travelling to the US. Despite the weak dollar ($2 to £1), the number of British visitors to America fell by 11% between 2000 and 2006, while travel to other countries such as India, New Zealand and the Caribbean has increased.
Discover America, the private body responsible for promoting travel to the US, estimates that the 17 % fall in tourism since 9/11 has cost America $94bn in lost tourist spending and 200,000 jobs.
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