Police have arrested three suspected members of al Qaida who had amassed explosives and may have been plotting attacks in Europe.

The three - a Russian, a Chechen and a Turk, according to Spanish police - were detained yesterday. 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.

The two arrested in Ciudad Real were taking a bus from southern Cadiz to the northern town of Irun, possibly intending to cross into France, the minister said. The pair had been in Spain for around two months.

"Police moved to arrest them when it became known that they planned to leave Spain," he said.

Fernandez Diaz did not disclose the identities of the three, but said two were suspected al Qaida operatives while the Turk was a facilitator.

He described one operative as a key member of the terror network, and said both operatives had practised flying in light aircraft. One was an expert in explosives and poisonous substances, he said.

Spanish police arrested dozens of al Qaida suspects since the September 11, 2001, attacks in the United States, and more after the 2004 train bombings in Madrid.

AP