Nabil al-Marabh, 34, who was arrested outside Chicago late Wednesday, has been linked both to two of the hijackers as well as to an operative of Mr bin Laden's Al-Qaeda organisation who is currently being held by Jordanian authorities.

Ahmed Alghamdi and Satam al-Suqami, hijackers on the two aircraft that crashed into the World Trade Center, have been linked to Mr al-Marabh by federal authorities, although the nature of the relationship has not been detailed.

Jordanian officials have also said Mr al-Marabh has ties with Raed M Hijazi, under arrest in Jordan for plotting attacks on Americans in the Middle East during the millennium celebrations - a plot that is believed to have been orchestrated by Mr bin Laden.

According to the New York Times, Mr Hijazi has told Jordanian authorities that Mr al-Marabh was also an operative of Al-Qaeda. If true, the arrest makes Mr al-Marabh the only known person with direct ties to Mr bin Laden network currently detained in relation to last week's terror attacks.

The FBI has been searching for Mr al-Marabh since at least Monday, when they stormed a Detroit apartment believed to belong to him. Instead, they found three men from North Africa who were holding false immigration documents and drawings of airports. The three were arrested on fake identification charges.

Although Mr al-Marabh, believed to be Palestinian, was on a list of more than 190 people sought by the FBI in connection with last week's strike, he has not been arrested on terrorism-related charges. In December, Mr al-Marabh was convicted in Boston of assaulting his roommate with a knife, but violated his probation. He is now being held on the knife charges.

Mr al-Marabh is believed to have lived in Boston for 10 years, where he worked for Boston Cab, a taxi company that has been tied to several bin Laden associates, including Mr Hijazi, who reportedly received explosives training at a bin Laden camp in Afghanistan.

Bassam A Kanj, a Lebanese national killed last year leading an attack by a militant Muslim group on the Lebanese army, also drove a cab for the company.

Robert Mueller, FBI director, said yesterday there was growing uncertainty whether the names of the 19 hijackers it released last week belonged to the men on board the planes. A senior Justice Department official said they were making sure the man arrested in Chicago was the man suspected of having ties to Mr bin Laden.

Officials in Saudi Arabia, where many of the hijackers' names apparently originate, have said some are aliases or stolen identities.

Number of missing, presumed dead, rises to 6,333

The number of people missing, presumed dead, in the World Trade Center attack has risen sharply to 6,333 from a previous estimate of 5,422, which had held steady since Tuesday, Lauren Foster reports from New York.

The bodies of 241 people have been recovered. Of these, 170 have been identified.

Rudolph Giuliani, New York mayor, said yesterday the main reason for the rise was "getting numbers from foreign nationals". He said the British consulate had reported 250 of its citizens were among the missing.

The mayor said the toll "may go up or down, depending on our checking it against possible duplication from other sources".

He also said 6,291 people had been treated for injury over the past nine days at local hospitals.

Rescue workers are still searching for survivors but hopes are fading. Mr Giuliani has acknowledged that the combination of the fire caused by the explosion of the two hijacked aircraft and the collapse of the twin towers make it likely that some victims' bodies will not be found.