Homeland Security Secretary Michael Chertoff told the BBC today that Europe could become a staging ground for terrorists determined to attack the United States.
(Chertoff) said militant attacks and plots in Europe over recent years had made the US aware of the "real risk that Europe will become a platform for terrorists".
Mr. Chertoff said it was likely security checks on travellers from Europe would be increased.
But he said steps would be taken to ensure travel and trade were not hit.
Chertoff explained European travelers present a security risk because of the U.S.' visa waiver program, which does not require Europeans to present a visa upon U.S. entry, leaving immigration officials with a narrow time frame to determine if a traveler's identification is fraudulent, and whether he or she presents a threat.
The International Herald Tribune reports Chertoff said no plans exist for requiring visas for Europeans entering the United States, although they may soon be required to register online before departure as part of an advanced authorization system.