Spain arrested 20 people yesterday suspected of recruiting Islamist fighters for Iraq, and said one of the recruits had killed 19 Italians in a suicide bombing in Iraq in 2003.
While there was no evidence the suspects planned any imminent attack in Spain, police thought they could have turned violent in future, Interior Minister Jose Antonio Alonso said.
"The police tell us that the organisation was very... structured and it cannot be ruled out that it might have committed violent actions in any European country, and of course in Spain, in future," he told a news conference.
Yesterday's arrests add to growing evidence that Iraqi militants have recruited fighters in several European countries to join the insurgency against the Iraqi government and the US-led forces supporting it.
French officials said last year at least five young men from a single Paris district had already died fighting in Iraq, one of them in a suicide attack. A 38-year-old Belgian woman blew herself up near Baghdad in November in what was believed to be the first suicide attack in Iraq by a European woman.
Last month, Spain arrested another 16 people accused of recruiting Islamist militants and a further two gave themselves up, although 12 were later freed pending further investigation.
The latest raids were aimed at two alleged al Qaeda-linked cells operating in the Madrid and Barcelona areas and the Basque country.
Police arrested 15 Moroccans, three Spaniards, a Turk and an Algerian accused of recruiting and providing financial and logistical support to fighters sent to Iraq.
They had connections in France, Belgium, the Netherlands, Algeria, Morocco, Turkey, Syria and Iraq, Mr Alonso said.
The Madrid cell, led by an Algerian trained in Afghanistan, supplied fighters to the network of Abu Musab al-Zarqawi, al Qaeda's leader in Iraq, the Interior Ministry said.
The ministry said the Barcelona-area cell was responsible for recruiting an Algerian suicide bomber who killed 19 Italians and nine Iraqis in an attack on an Italian police base in southern Iraq in November 2003.
Laboratories run by Spanish and Italian security forces had worked together to prove this link, it said in a statement.
The Nassiriya attack was the deadliest on Italian forces since WWII and caused deep shock in Italy.