Police have arrested three suspected members of al-Qaida who had amassed explosives and may have been plotting attacks in Europe, Spain's interior minister said Thursday.

The three — a Russian, a Chechen and a Turk, according to Spanish police — were detained Wednesday. The Turk was arrested in the southern town of La Linea, while the other two were picked up in the central town of Ciudad Real.

Enough explosive material was found in the house in La Linea to blow up a bus, and the material could be especially dangerous if combined with shrapnel, Interior Minister Jorge Fernandez Diaz said.

"This is one of the most important operations carried out against al-Qaida," Fernandez Diaz told reporters. He said the operation involved close collaboration with intelligence services from "Spain's allies."

Spanish authorities had been watching the suspects for "some time," the minister said, without giving further details.