Six men, including radical Muslim Abu Izzadeen, were arrested yesterday over speeches made at a mosque two-and-a-half years ago.
Scotland Yard said the men were detained in an investigation into incitement of others to commit acts of terrorism overseas and terrorist fund-raising.
The men, aged between 21 and 35, were held at addresses in east London, Southall and Luton at around 5am on Tuesday.
The speeches were allegedly made at a mosque in London in November 2004.
A Yard spokesman said a number of searches were ongoing in connection with the investigation.
"The arrests form part of a long-term pro-active and complex investigation into alleged incitement and radicalisation for the purposes of terrorism, as well as alleged provision of financial support for international terrorism."
O utspoken Muslim scholar Anjem Choudary confirmed his "close friend" Izzadeen had been arrested.
"All these arrests must be seen in the light of the crusade which the Blair regime has launched against the Muslim community, trying to justify their foreign policy through demonising Muslims, and targeting Muslims who have the fortitude to speak up," he continued.
"Abu Izzadeen and other individuals are completely innocent, they do not support any terrorist activities, in this country or abroad."
Luton, Bedfordshire, was where July 7 bomber Jer-maine Lindsay met the other three suicide attackers before taking a train to London.
