ROME, Italy (CNN) -- Police made a string of arrests across Europe Tuesday, detaining 20 people suspected of involvement in the recruitment of suicide bombers, Italian police said.



Eleven of the arrests were in Italy, in the northern cities of Milan, Reggio Emilia, Bergamo, and San Remo, said. Lt. Col. Sandro Sandulli, the head of the Carabinieri special forces. One was already in custody, so authorities served him with a new arrest warrant which included new charges against him, Sandulli said.



Three arrests were in Britain, one in France, and one in Portugal, Sandulli said. The remaining arrests happened in European countries but Sandulli did not specify which ones.



Those arrested are suspected of forming Salafi Jihad terrorist cells which were recruiting suicide bombers and sending them to Iraq and Afghanistan, said Col. Mario Parente, deputy commander of the Carabinieri special forces unit.



Parente said that during the arrests, police found al Qaeda manuals for the production of explosives, detonation devices, and various poisons. He said the manuals also included details of guerrilla-style war operations.



Salafi is an extreme school of Islamic thought which developed in Egypt and began to have prominence with militant groups there in the late 1960s and has since been adopted by terrorist groups in North Africa, the Middle East, and Europe, said Sajjan Gohel, director of international security at the Asia Pacific Foundation in London.



"It's become the ideology of choice for transnational terrorism, including al Qaeda," Gohel said. "It's emerging as a very dangerous ideology."



The Madrid train bombers and various terrorist cells in Italy were part of the Salafi school of thought, he added.



Italian police said Tuesday's arrests were the result of an investigation, started in 2003, into some Salafi cells which were organized by Tunisians and Algerians. The main suspect in the operation is a Tunisian who was arrested in 2002 during a separate antiterrorism operation, police said.



The main terrorist cell was based in the northern Italian region of Lombardy and involved what investigators called a "long-term" jihadist program which provided military and ideological training.



Another cell, based in Reggio Emilia, had the goal of creating a grand Islamic "empire" stretching from Morocco to China, police said.



Parente said those arrested are also accused of producing false documents, facilitating illegal immigration, and covering up other individuals wanted for terrorism-related crimes. E-mail to a friend



CNN's Flavia Taggiasco in Rome contributed to this report
What group did the suspected work for? What were they recruiting for? What nationality are the 20 suspected? What are those held accused of? Where were they going? Where were they all caught? what happened in italy? what was the total of people held What regions did the arrests take place?
Salafi Jihad terrorist cells suicide bombers, Tunisians involvement in the recruitment of suicide bombers, Iraq and Afghanistan, Europe arrests 20 across Europe
question: What group did the suspected work for?, answer: Salafi Jihad terrorist cells | question: What were they recruiting for?, answer: suicide bombers, | question: What nationality are the 20 suspected?, answer: Tunisians | question: What are those held accused of?, answer: involvement in the recruitment of suicide bombers, | question: Where were they going?, answer: Iraq and Afghanistan, | question: Where were they all caught?, answer: Europe | question: what happened in italy?, answer: arrests | question: what was the total of people held, answer: 20 | question: What regions did the arrests take place?, answer: across Europe