[The process] may well have contributed to the fact that we have not suffered a substantial terrorist attack since 11 September

John Ashcroft, US Attorney General

Mr Ashcroft said the first phase, begun last November, had provided valuable intelligence on terror activities in America.

Civil liberties groups and Arab American leaders denounced the step as racist, as the interviews mainly focused on Arab and Muslim visitors.

Mr Ashcroft said the next batch would involve "men who come from a variety of settings and whose passports reflect a variety of settings where there have been strong al-Qaeda presences".

He said the interviews would be voluntary and would be completed within two months.

'Produced results'

According to a report released by the Justice Department, the first round of interviews produced what Mr Ashcroft called "many sources and leads".

Arab American groups have criticised the strategy

Investigators are said to have learned the name and address of a person connected to the 11 September hijackers, and details of individuals who received flight training at the Florida centre used by the terror suspects.

The attorney general said the approach "may well have contributed to the fact that we have not suffered a substantial terrorist attack since 11 September".

Mr Ashcroft said fewer than 20 people who were interviewed were detained, mainly for immigration violations, and none for terrorist connections.

However, critics said the interview process stirred racial tension.

"Those interviews created deep strains between law enforcement and recent immigrants who are Arab and-or Muslim," said James Zogby, president of the Arab American Institute.

Mr Ashcroft denied the allegations, saying investigators "fostered new trust" with Arab and Muslim communities.

The attorney general admitted the authorities had only been able to find half of the original 5,000 people wanted for interviews and had little idea where the remainder were.