Italian police have arrested 20 foreigners suspected of terrorist activity.
During the operation, ordered by prosecutors in Milan and carried out in northern Italy and abroad, police said they seized poisons and ignition devices for explosives.
Police believe those arrested have been setting up Islamist cells that recruited and assisted would-be suicide bombers in Iraq and Afghanistan.
British police arrested two men after Italian authorities made a request for their extradition on charges related to the inquiry.
Ali Ben Zidane Chehidi (34) was arrested in Croydon, near London and Mohamed Salah Ben Hamadi Khemiri (53) was arrested in Manchester.
"The two men were arrested on behalf of the Italian authorities under an extradition warrant in relation to allegations that between 2003 and 2005 they forged documents to facilitate the illegal entry into Italy of recruited volunteers to fight jihad in Iraq and Afghanistan," police said in a statement.
The men were due to appear before magistrates later today.