Ashcroft: Arrests designed to protect Americans
It is the first time the American authorities claim to have caught any members of Osama Bin Laden's network.
His announcement was the first official accounting of those in custody for several weeks, since it became known that 1,100 people had been arrested since the 11 September attacks on New York and Washington.
Mr Ashcroft rejected charges that civil rights were being violated in the hunt for suspected terrorists
Immigration charges
"A number of the individuals that are being detained... are suspected terrorists," John Ashcroft told reporters.
"With arrests and detentions, we have avoided further terrorist attacks... America's defences have grown stronger."
Of those in custody, Mr Ashcroft said that 104 people had been formally charged with federal crimes, of whom 55 remain in custody.
Another 548 remain in custody on immigration charges - some have also been charged with federal crimes.
It is thought that the majority of those detained, most of whom have not been named, are of Middle Eastern descent.
Human rights concerns
Mr Ashcroft responded to criticism that the detention of the suspects, and the withholding of their names, has contravened their human rights.
"I am not interested in providing, when we are at war, a list to Osama Bin Laden and the al-Qaeda network of the people we have detained that would make any easier their effort to kill Americans," he said.
But Lucas Guttentag, of the American Civil Liberties Union, said more information needed to be released about those in detention.
"It is ironic that the government is now concerned about rights when it has arrested and jailed hundreds of people without giving the American public any proof that the detainees are being treated fairly," he said.
Mr Ashcroft also said that those held on suspicion of terrorist activity would not have their legal counsel paid by the federal government.