Ramzi Binalshibh - now in custody in Pakistan - is allegedly one of the most senior al-Qaeda members to be arrested over the past year.

US Attorney General John Ashcroft named him among the most wanted suspects within weeks of the 11 September attacks on the United States.

Mr Binalshibh - a Yemeni national - was recently quoted as saying he helped plan the operation.

Western intelligence officials believe he is the missing link - the one person who can put all the pieces of the al-Qaeda strategy into context.

Key meetings

Mr Binalshibh, who is 30, is said to have become a key member of the al-Qaeda cell in Hamburg, Germany, after seeking asylum there in the late 1990s.

Moussaoui's indictment mentions Binalshibh

According to officials, he met Mohammed Atta, the leader of the Hamburg cell and one of the alleged masterminds of the 11 September attacks, through a local mosque in 1997.

The two men are said to have become roommates and, over the next two years, to have engaged in radical Islamic activities.

In an interview with the Arab TV station al-Jazeera, Mr Binalshibh said he and other members of the Hamburg cell travelled to Kandahar in Afghanistan in late 1999 to receive training.

There, according to the interview, they met many of the key players in the 11 September attacks.

Mr Binalshibh is the only person believed to have attended both of the crucial meetings held to plan the operation, one in Malaysia and the other in Spain.

He handled logistics and money matters for the attacks and entered Pakistan just before 11 September, US officials say.

Previous attacks

Mr Binalshibh would have been among the hijackers who carried out the attacks, had he not tried and failed four times to obtain a US visa, according to investigators.

His place was reportedly taken by Zacarias Moussaoui - the only person to have been charged in the United States in connection with the attacks.

Mr Moussaoui was allegedly sent money by Mr Binalshibh.

Intelligence officials say Mr Binalshibh may also have been involved in two other operations blamed on al-Qaeda.

One was the suicide attack in Yemen on the USS Cole, an American destroyer, in which 17 sailors died in 2000.

The other was the attack on a Tunisian synagogue earlier this year, in which 14 German tourists were killed.