Pakistani intelligence has captured letters purportedly written by bin Laden in recent weeks and showing that he was actively guiding the terrorist network. Pakistani security officials said that the arrest of Khalid Sheikh Mohammed, the suspected mastermind of the September 11 attacks, had provided vital information about al-Qaeda’s links in Pakistan and other countries.

Some documents recovered in the raid on a house in Rawalpindi last weekend showed that Mohammed was in contact with bin Laden. It is not clear, however, whether they had met recently. A second al-Qaeda suspect, Mustafa Ahmed Hawsawi, a Saudi Arabian national who allegedly financed the September 11 plot, was also arrested.

American intelligence officials are following leads, including mobile phone numbers obtained from the raid, that they believe may lead to al-Qaeda operatives in the US.

In Washington the arrest of Mohammed and Hawsawi has raised the prospect of America being able to stage a Nuremburg-style show trial of those who masterminded the September 11 attacks. Already in US custody are Ramzi bin al-Shibh and Abu Zabaydah, al-Qaeda linchpins said to have played a key role in the plot.

Some US officials see the four as offering a chance to prove that the investigation into the terrorist attacks has born fruit, enabling Americans to try to draw a line under the experience.

The most likely vehicle for such a trial would be the military tribunals announced by President Bush in 2001. Although US officials initially suggested that the tribunals would be in private, recent Pentagon guidelines show that they can be open, with the most sensitive proceedings held behind closed doors.

The White House, perhaps sensitive that such a trial could take place in a presidential election year with Mr Bush bidding for a second term, held the idea at arm’s length. Ari Fleischer, Mr Bush’s spokesman, said that any decision on the form of such a joint trial would be taken not in the Oval Office but at the Pentagon. However, US officials did not rule out the idea.

In Pakistan investigators have obtained crucial information from Asadullah Rahman, the son of Abdur Rahman, the blind Egyptian cleric convicted of the 1993 bomb attack on the World Trade Centre.

Rahman was arrested in Quetta in southwestern Baluchistan province two weeks ago. His capture provided not only crucial information that led to the arrest of Mohammed but also information about al-Qaeda’s network in Pakistan. “We are closing in on other al-Qaeda leaders still hiding in the region,” a senior Pakistani official said.

Security officials suspect that the rugged mountainous Baluchistan region bordering Afghanistan’s southwestern province has become the centre of al-Qaeda’s activities over the past few months. The area is a stronghold of Islamic parties that are part of the coalition governing the province. Heavy fighting between the remnants of Taleban and American forces has taken place in recent weeks in the Afghan area across the border.

Pakistani officials did not rule out the possibility that the al-Qaeda leader is hiding in the strategically placed province. It also borders Iran, into which many al-Qaeda fugitives are thought to have crossed.

The coming to power of radical Islamic parties has provided a positive atmosphere and support for the al-Qaeda operation in the region. Maulana Fazalur Rahman, leader of a five-party Islamic alliance — and a candidate for Prime Minister — has said that bin Laden is alive and has vowed to protect him. He said that Pakistani Muslims considered the Arabs to be Islamic warriors and called on the military-backed Government to stop operations against them.

The powerful Islamic alliance is locked in a confrontation with the Government after Mohammed and Hawsawi were arrested in a Rawalpindi house belonging to a woman leader of Jamat-i-Islami, a key alliance member.

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