The FBI has offered a $5m bounty for Atef

He may have been the man UK Prime Minister Tony Blair referred to when he said: "Since 11 September we have learnt that one of Bin Laden's closest and most senior associates was responsible for the detailed planning of the attacks."

Before joining forces with Bin Laden, Atef was an Egyptian policeman and member of Egyptian Islamic Jihad.

Sadat assassination

The group assassinated President Anwar Sadat in 1981 as retribution for agreeing peace with Israel.

He fled Egypt during the subsequent security crackdown, seeking refuge with Bin Laden in Sudan and then Afghanistan.

He has been a close aide to Bin Laden for more than 10 years.

US bounty

The US has offered a reward of $5m for his capture.

US prosecutors have accused him of encouraging attacks on American forces in Somalia in 1993 in which 18 died.

He is also alleged to have directed the bombers who struck embassies in Kenya and Tanzania in 1998, killing 224 people and injuring thousands of others.

President George W Bush included Atef in an order freezing terrorist assets.

His name has also appeared in the indictment and transcripts at the trial in Manhattan of four men jailed for life for their parts in the attacks on the US embassies earlier this year.

US prosecutors allege that his primary responsibility is to train al-Qaeda recruits.

The ties between Bin Laden and Atef are believed to have become even closer when the Bin Laden's 19-year-old son married Atef's daughter earlier this year.