Spanish police have arrested eight Moroccan men accused of harbouring Islamic extremists, including several suspects in the Madrid bombings of 2004, and helping them flee the country.

The interior ministry said officers made the arrests in pre-dawn raids in four northeastern towns near Barcelona, as well as Madrid and Algeciras in the south.

The arrests stemmed from a 2005 police operation during which Spain broke up a cell that allegedly recruited people to stage suicide attacks against US-led forces in Iraq and other targets set by al-Qaeda, the ministry said in a statement.

The men were detained on the orders of Baltasar Garzon, one of Spain's most senior judges. 

Islamic extremists have claimed responsibility for the Madrid attack, saying they had acted on behalf of al-Qaeda to avenge the presence of Spanish peacekeeping troops in Iraq.

However, Spanish authorities say they have found no evidence that al-Qaeda ordered or financed the attacks.

Spanish investigators have said one of the fugitive suspects in the Madrid attacks, Moroccan Mohamed Afalah, is believed to have died in a suicide attack in Iraq in 2005.

A confidential police report quoted in Spanish newspapers has said another suspect, Daoud Ouhnane of Algeria, also died in Iraq while fighting coalition forces.

Since the September 11, 2001 attacks in New York and Washington, Spanish police have arrested hundreds of Muslims, many in connection with the Madrid attack.

In recent years police also have focused on cells suspected of collecting money to finance al-Qaeda-linked groups abroad.