US authorities are investigating a suspected visa scam which may have allowed 71 people - including some with links to the 11 September attackers that the US blames on the al-Qaeda network - to have entered America illegally.

At least one former employee of the US embassy in Qatar has been questioned about alleged bribery, reports say.

There are a lot of safeguards and checks. But we don't have our facts. It is still under investigation

US official

The FBI has detained 31 people suspected of entering the US with visas illegally obtained at the embassy, US State Department spokesman Philip Reeker said.

He said that investigators were still looking for 29 more people who had received suspect visas.

Six others are believed to have left the US and five others believed to have entered the US illegally are spouses or children of a visa holder, Mr Reeker said.

Other officials, quoted by the AFP news agency, said that the investigation dubbed "Operation Eagle Strike" had identified 39 Jordanians, 28 Pakistanis, three Bangladeshis and one Syrian who had received visas from the embassy in Doha between July 2000 and May 2001.

The officials said those who had been detained since 24 June were 25 Jordanians, five Pakistanis and one Syrian.

Three are believed to have links with the 19 hijackers who took part in the 11 September attacks, the officials said.

Hijackers' room-mate

The three include Ramsi Al-Shannaq, a Jordanian who has admitted being a room-mate of two of the hijackers.

He was arrested in Baltimore on 24 June and charged with illegally obtaining a US visa.

At a court hearing in Baltimore on Wednesday, Assistant US Attorney Harvey Eisenberg said that Al-Shannaq, 27, had been denied visas four times before paying $13,000 for an illegal one.

Mr Eisenberg said Al-Shannaq was part of a bribery ring that involved pay-offs of more than $13,000 per person.

Bail granted

However, Magistrate Susan Gauvey ordered that Al-Shannaq be released on conditional bail, saying that there was no evidence he had anything to do with the 11 September attacks.

Her ruling was upheld on appeal.

A US official told AFP that the purpose of Operation Eagle Strike was to determine how the visas had been obtained and if terrorists had used them to plot attacks against the United States.

Another unnamed US official told the Associated Press: "We don't know exactly how it was accomplished.

"There are a lot of safeguards and checks. But we don't have our facts. It is still under investigation."