US Attorney General, Mr John Ashcroft announced yesterday that federal agents will be flying on commercial jetliners to guard against further terrorist acts.
He said officers believe there is a continuing threat because "associates of the hijackers that have ties to terrorist organisations may be a continuing presence in the United States".
Mr Ashcroft directed the US marshals service to assign more than 300 deputies to assist the FBI in the terrorism probe.
From enhanced wiretapping authority to stiffer penalties for those who harbour terrorists, the Bush administration is asking Congress for sharper tools to help solve last week's terrorist attacks.
Congressional leaders emerged from FBI headquarters on Sunday saying they were pleased with the progress of the investigation. The Justice Department disclosed that warrants for material witnesses are currently being worked on.
At least two arrests have been made. The first was of a man at John F. Kennedy International Airport who had a fake pilot's licence. No details were released on the second.
Mr Ashcroft and FBI director Mr Robert Mueller stressed the importance of swift action on the new legislation. "We need to upgrade US law because federal law enforcement agencies have better tools against organised crime and illegal gambling than we do against terrorists," Mr Ashcroft said.