In a written statement, the Saudi Interior Ministry said the Saudi cell's leader was found with a letter from al-Qaida's second in command, Ayman al-Zawahiri, "urging him to raise funds and that he (al-Zawahiri) will provide him with the personnel, whom they called the mujahedin ."

The ministry claimed that referred to fighters coming from Iraq, Afghanistan and North Africa using the cover of pilgrims visiting the Holy Mosque and other Saudi destinations, CNN reported Wednesday.

"They had already begun planning to target oil installations and other security locations with car bombs," the Saudi ministry said.

But critics of Saudi Arabia suggest there is little or no way to determine the justness of the accusations.

Christoph Wilcke, a researcher for Human Rights Watch, said some of those arrested in the past have had few ties to terrorist groups.

"Effectively, Saudi Arabia operates its own Guantanamo," he said. "Saudi security services operate a string of prisons where these kind of people go in, along with your ordinary dissident, and nobody will ever hear from them again."