John Ashcroft, US attorney general, said on Wednesday that federal authorities had uncovered evidence that a number of foreign states have supported the terrorist network that carried out last week's attacks on New York and Washington.

Refusing to name any countries, Mr Ashcroft said the Justice Department had determined the terrorist groups had been "harboured and supported, sustained, protected by a variety of foreign governments".

"The United States of America will not tolerate that kind of support," he said.

Iraqi authorities denied any involvement in the strikes, saying on Wednesday that its intelligence agents never met Mohammed Atta, the 33-year-old Egyptian named by the FBI as one of the hijackers. US officials said on Tuesday they had received information that Mr Atta met Iraqi intelligence agents in Europe earlier this year, but they had not been able to confirm the report.

Mr Ashcroft also said it remained unclear whether the first criminal arrests in the investigation, made late on Tuesday in Detroit, constituted a "major breakthrough" in the case.

Three men were arrested in a Detroit apartment with fake passports and drawings of airports when FBI agents entered looking for a different person, who was on a list of more than 190 people suspected to have information on the attacks.

The FBI said the men, Farouk Ali-Haimoud, 21, Ahmed Hannan, 33, and Karim Koubriti, 23, had identification badges for an airport food service company and had hand-written diagrams of "an airport flightline", including planes and runways.

The three, Moroccan and Algerian nationals who have been charged with conspiracy and possessing false documents, join 75 people being held by federal immigration authorities in connection with the inquiry.

The Justice Department has broadened the powers of the Immigration and Naturalisation Service to detain immigrants suspected of crimes indefinitely during national emergencies. Mr Ashcroft is expected to seek even broader powers this week, which may include the ability to arrest and deport foreigners connected with terrorist acts without presenting evidence publicly.

According to a two-page outline of the legislation obtained by the Financial Times, which lacks key details and could change before being sent to Capitol Hill, the bill will include provisions keeping accused terrorists in jail by default and making detention of suspected terrorists "mandatory". Police would also be able to conduct more wiretaps and use e-mail surveillance systems in more situations without court orders, and for longer times. The bill would permit sharing of surveillance information with foreign governments.

Although civil liberties groups have raised concerns, Mr Ashcroft defended the package, saying his department would have "strict regard for every safeguard of the US constitution".