MADRID, Spain (CNN) -- Spanish Civil Guards arrested six Pakistani nationals Tuesday, accused of sales tax fraud, a Civil Guard spokesman in Madrid told CNN.
The spokesman declined to confirm Spanish media reports that the suspects may have been involved in financing Islamic extremist activities.
But the arrests occurred across Spain in an operation directed by Spain's anti-terrorism National Court.
The suspects were detained in Barcelona, the southeast region of Valencia, the northern city of Logrono and in Las Palmas on Spain's Gran Canaria Island in the Atlantic, off the coast of Morocco, said the Civil Guard spokesman, who by custom is not identified.
Since the Madrid train bombings in 2004 that killed 191 people and wounded more than 1,800 --- which a court found was due to Islamic terrorists --- Spanish police have arrested numerous suspects for financing Islamic terrorism.