Details emerged Sunday of raids in which Spanish police say they arrested 12 Pakistanis and two Indians who were "learning to build bombs" when police burst into one apartment.

The 12, detained in several Barcelona apartments in the early hours of Saturday, belonged to a terrorist cell planning an attack, an official was quoted by El Periodicio de Catalunya as saying.

"When police arrived, a group of them in one apartment were being taught how to build bombs," the interior ministry official was quoted by the newspaper as saying.

The raids were a chilling reminder to Spaniards that their country apparently remains the object of terrorist attack four years after the devastating bombings that left 191 people dead in Madrid.

Since those attacks on four suburban trains, some 400 suspected Islamist terrorists have been detained in Spain amid repeated calls from al-Qaeda leaders to "liberate from the infidels al Andus", as Spain was known during 800 years of Arab rule in the Middle Ages.

Up to now the main terrorism threat has come from North Africa, where Islamist groups are believed to have gained an increasingly firm foothold in Algeria, Morocco and Mauritania.

This time, however, the tip-off to secret service agents apparently came from Pakistan, from where a group of Islamists were reported to have arrived in Barcelona.

"If someone has fuse timers in his apartment, we have to assume he was planning violence of some sort," Interior Minister Alfredo Perez Rubalcaba said after Saturday's arrests.

Press reports said those detained had arrived mostly from Morocco and Algeria. However, the fact that Pakistani nationals were apparently involved in planned violent acts was something new.

Investigators were quoted in Spanish press reports as saying the development had to do with the Taliban making progress in Afghanistan.

"Afghanistan is back as the big centre for training al-Qaeda terrorists, as it had been before US-led troops moved in," one investigator was quoted a saying by El Pais newspaper.

More and more Pakistanis who live in Spain were going to Afghanistan for training, he added.

Barcelona is home to some 15,000 Pakistanis - most of them in the Raval district close to the landmark Las Ramblas avenue which passes through the old town to the port. However, Pakistani community leaders have been quick to jump onto the defensive.

"I would be very surprised if these people had anything to do with terror," said Pakistani Workers' Association President Javed Ilyas. "They were in the act of praying when police burst in."