By Kevin Anderson BBC News Online Washington correspondent

US Attorney General John Ashcroft has defended a decision to give the FBI expanded investigative powers to monitor the activities of people and organisations suspected of plotting terrorist acts.

In response to questions of whether the changes amounted to domestic spying, Mr Ashcroft said the new powers would only be used to detect and prevent terrorism.

But civil liberties groups denounced the expanded powers, and the announcement outraged some veterans of the protest movement against the Vietnam War who were targets of FBI surveillance more than 30 years ago.

The abuses that have been alleged about the FBI decades ago would not be allowed

US Attorney General John Ashcroft

FBI agents will now be able to monitor people at any public event or place if they suspect a terrorist plot, and they do not need to seek approval from FBI headquarters.

However, Mr Ashcroft said that the FBI will not be allowed to develop files on anyone, and searches for information or evidence still will require a warrant approved by a judge.

It was the first change to the FBI's investigative guidelines in 25 years. The last changes came following the revelations of the FBI's COINTELPRO programme aimed at political dissidents and dissident groups in the US.

"The abuses that have been alleged about the FBI decades ago would not be allowed," Mr Ashcroft said.

'Fishing expeditions'

The American Civil Liberties Union (ACLU) said the new powers would allow the FBI to go on "fishing expeditions" without a scintilla of evidence.

It added that the Bush administration should instead investigate why US authorities failed to foresee the attacks.

Before the new guidelines, [agents] could not do the kind of information gathering that you or I could do as private citizens

Roger Pilon, Cato Institute

"The government is rewarding failure," said Laura W Murphy, director of the ACLU's Washington National Office.

"When the government fails - as it increasingly appears to have done before 11 September - the Bush administration's response is to give itself new powers rather than seriously investigating why the failures occurred," she said.

The ACLU warned that the new guidelines would allow the FBI to freely infiltrate mosques, churches and synagogues, to listen in on online chat rooms and read message boards, even if it has no evidence that a crime might be committed.

But Roger Pilon, vice-president of legal affairs at the libertarian Cato Institute says 11 September was a "wake-up call".

He added that the excesses under J Edgar Hoover were illegal under the new investigative guidelines, as they were under the old guidelines, and that restrictions on the FBI put in place 25 years ago were excessive.

"[Agents] could not do the kind of information gathering that you or I could do as private citizens," he said.

FBI excesses

Burton Caine is a law professor at Temple University in Philadelphia - in the 1960s and 1970s, he represented war protesters and draft dodgers.

The FBI monitored anti-war and civil rights protesters

He remembers the FBI surveillance during a peaceful protest march in 1970 from City Hall to Independence Hall in Philadelphia.

They took the names of the marchers and the names of their organisations, he said, adding that he had clients that were the targets of FBI wiretaps.

"That gets about as close as you can get to scaring people just for exercising their civil rights," he said.

"And you have Ashcroft wanting to do it all over again."

Instead of expanding powers for the FBI, the bureau needs to become more efficient, and he is wary of expanding the bureau's powers of surveillance.

"There is no doubt enemies are in our midst," he said, but added that we rely on government to prevent terrorism not to spy on its people.