RIYADH, Saudi Arabia - Police arrested 172 suspected Islamic extremists, some of whom had trained abroad as pilots so they could fly aircraft in attacks on Saudi oil fields, the Interior Ministry said yesterday. A spokesman said all that remained in the plot "was to set the zero hour."

The ministry issued a statement saying the detainees were planning to carry out suicide attacks against "public figures, oil facilities, refineries . . . and military zones" - some of which were outside the kingdom.

"They had reached an advance stage of readiness, and what remained only was to set the zero hour for their attacks," an Interior Ministry spokesman, Brig. Mansour al-Turki, said in a telephone interview. "They had the personnel, the money, the arms. Almost all the elements for terror attacks were complete except for setting the zero hour for the attacks."

The suspects were detained in separate waves, he said, with one group confessing and leading security officials to the next group, as well as weapons caches.

The ministry did not say the plotters would fly aircraft into oil refineries, as the Sept. 11, 2001, hijackers flew planes into buildings in New York and Washington, but its statement said some detainees had been "sent to other countries to study flying in preparation for using them to carry out terrorist attacks inside the kingdom."

They also planned to storm Saudi prisons to free the inmates, the statement said. More than $5.3 million was seized in the operation, one of the largest sweeps against terror cells in the kingdom.

The Saudi statement said some of the military targets were outside the kingdom. Turki said the arrests occurred "at various and successive times," but he did not elaborate.

The Saudi state TV channel Al-Ekhbariah broadcast footage of a weapons cache found buried in the desert. The arms included bricks of plastic explosives, ammunition cartridges, handguns and rifles wrapped in plastic sheeting.