The British government has warned the aviation industry of a possible al-Qaeda attack in a letter outlining the heightened risk, the BBC said today.
A security source said that counter-terrorism advice to the transport sector had been updated to indicate a possible heightened threat of attack, based on monitoring of suspected terrorists, although there was no sign of an imminent assault.
The BBC said it had obtained a letter from the Department of Transport addressed to the air transport sector.
"There are indications that al-Qaeda may be considering an attack against a UK airport or aviation sector target," the BBC said, quoting the letter.
The letter said that "the economic, political and psychological significance of the UK aviation sector coupled with the large crowds present within some of its major assets would enable a successful attack to fulfil al-Qaeda's objectives".
The BBC said the letter, however, emphasised that no changes to security measures had been made as a result and that the planned method of attack was unclear.
A senior Iraqi official said last month that he believed al-Qaeda was planning attacks in the United States, Britain and Europe around Christmas, one year after a failed attempt to bomb a US-bound airliner.
British police and security services have investigated dozens of suspected plots and arrested hundreds of suspects since the September 11, 2001 attacks on the United States.
The UK Department of Transport declined to comment on the report. Police said earlier the national threat level in Britain remained at "severe", the second highest, meaning an attack was highly likely. It was raised a year ago.
Fifty-two people were killed in London in 2005 when four British Islamists blew themselves up on underground trains and a bus.
The Metropolitan police, responsible for coordinating counter-terrorism operations nationally, also said that it had no knowledge of a separate threat gauge for airports and railway terminals being raised from "substantial" to "severe".
Threat levels for specific national infrastructure sectors are not normally made public.
The British Transport Police had also earlier played down suggestions of a heightened state of security.
The British Home Office (interior ministry) said that if there was any intelligence of an imminent threat or a plot under way the threat level would be raised to "critical", its highest level.
Reuters