Interpol issued an arrest warrant yesterday for Ayman al Zawahri, an Egyptian-born surgeon reported to be Osama bin Laden's deputy.
Zawahri, 51, is said to be the leader of al Jihad, a militant group based in Egypt, and a key figure in Mr bin Laden's al-Qa'ida network, blamed by America for orchestrating this month's terrorist attacks.
Meanwhile, British anti-terrorist officers were questioning three men arrested during house raids in Leicester yesterday morning. The arrests were not believed to be directly linked to the terrorist attacks in New York, Washington and Pennsylvania, but may be connected to European "cells" of Islamic fundamentalist terrorists.
News has also emerged that American investigators, trying to track down accomplices of the teams who hijacked passengers jets on 11 September, are growing increasingly frustrated at drawing a blank in their inquiries.
In a joint operation yesterday morning, members of MI5 as well as officers from Scotland Yard's anti-terrorist branch and Leicestershire Constabulary arrested the three men under the Terrorism Act 2000.
The men, one aged 29, another in his 20s and a 35-year-old, were in custody at a Leicestershire police station.
Police were making extensive searches of two houses in Rolleston Street and Prospect Hill both in the Spinney Hills area of Leicester.
Yesterday's raids follow intelligence passed to the British authorities by European security agencies investigating the activities of suspected Islamic terror groups in Belgium and France. They will add to concerns that Britain is a staging post and recruiting ground for Islamic terror organisations.
The families of several French terrorist suspects have recently blamed fanatical elements in Britain for "brainwashing" them. The family of David and Jerome Courtellier, brothers who were among seven people arrested in France last Friday in relation to an alleged plot to attack the US embassy in Paris, claimed they were recruited by Islamic extremists while living in London.
The Courtellier brothers are believed to have stayed in a flat in Brixton, south London, with a man whom American investigators suspect intended to be a suicide hijacker in the 11 September attacks.
Zacarias Moussaoui, a French-Moroccan who lived in Brixton until February, was arrested in Minnesota in August after raising suspicions at a flight training school when he told staff he did not require lessons on landing or take-off.
Mr Moussaoui is being held by the FBI. His mother claims he became fascinated with fundamentalism after living in London for 10 years.
But, in America, despite a massive manhunt by federal agents, and hundreds of detentions of possible suspects, there has been just a handful of arrests, none of them directly relating to the core conspiracy.
Yesterday's New York Times quoted an unnamed senior law enforcement official saying the investigation has yet to identify a single direct accomplice of the 19 men who hijacked the airliners on 11 September.
The official added that the most promising leads were coming out of Germany, suggesting the network had its origins there and used the United States only for forward deployment. One particularly pessimistic theory circulating in the FBI is that the 19 men destroyed the key evidence by killing themselves and ensuring their bodies were at the heart of the airliner fires.
One man initially thought to be a key contact of the hijackers in San Antonio, Albader Alhazmi, was released on Monday without being charged. He had been named as a material witness. Also on Monday, authorities in Virginia said they had arrested two men who helped three of the hijackers obtain fraudulent state driving licences. The New York Times said, however, that the two almost certainly knew nothing of the hijackers' ambitions.
Another potentially crucial arrest, of a former Boston cab driver called Nabil al-Marabh, has been similarly anti-climactic so far. Investigators have not yet been able to confirm the man is the same one they suspect of having links to Mr bin Laden and his network.Reuse content