The director of US homeland security has said the United States is still preparing for possible terrorist attacks.
Tom Ridge made his comment after a tape, purported to be from one of Osama Bin Ladens key advisors, was aired on Arabic television warning the United States that there will be a 'high price' to pay if it harmed detainees at Guantanamo Bay.
The US is holding more than 600 alleged al-Qaeda and Taleban fighters at the Cuban base.
Mr Ridge said a new advisory had been sent out to ferry operators in the US, warning of possible attacks.
His department last week warned the airline industry that the threat of possible attacks would last until at least the end of summer.
