U.S. Homeland Security Secretary Michael Chertoff said on Wednesday that one of the biggest threats to U.S. security may now come from within Europe.
In an interview with BBC radio, Chertoff said that American authorities were becoming increasingly aware of a real risk of Europe becoming a "platform for terrorists".
He said it was important to step up security checks on passengers coming from Europe to the United States.
"One of the things we have become concerned about lately is the possibility of Europe becoming a platform for a threat against the United States," Chertoff said.
"We have watched the rise of home-grown terrorism," he added, citing the Madrid train bombing in March 2004 and recent foiled plots in Britain and Germany.
"That suggests to us that the terrorists are increasingly looking to Europe both as a target and as a platform for terrorist attacks."
Chertoff's comments came after reports that British intelligence services are investigating an Islamist Web site which said that a branch of al Qaeda had been established in Britain.
Security experts fear a posting on the site, urging young Muslim men to rise up against what it called infidels such as Prime Minister Gordon Brown and former Prime Minister Tony Blair, may be genuine.
Chertoff said that while Washington had no plans to suspend a visa waiver programme that allows most Europeans who travel to the United States as tourists to do so without a visa, authorities would like to step up advance checks on travellers.
"We do want to elevate some of the security measures in the programme," he said, proposing an advance travel authorisation system which would require potential visitors to register online their intention to travel to America to allow authorities to clear them in advance.
Chertoff also said that the absence of any attacks in the United States since September 11, 2001 had created "a certain sense of complacency" which needed to be dispelled.
"When I lift my eyes and look around the world and I look at what happens in Britain and Germany and Spain and Bali and Pakistan, I don't see terrorism going away, I see an al Qaeda that's emboldened, he said.
"I don't see any diminishment of the threat and my concern is that we not relax and let the enemy get ahead of us."
Source: Reuters (English)
See also: US: European Islamists present a threat