Saudi Arabia is holding 520 suspected militants following raids across the kingdom this year, its interior ministry says.
They are accused of links to what it called the "deviant group" - a term used for al-Qaeda by Saudi officials.
They said the accused were of various nationalities and had been plotting attacks in and outside Saudi Arabia.
Officials said a further 181 suspects detained in 2008 had been released because of a lack of evidence.
The militant arrest figures are thought to be the largest and most comprehensive ever released by the Saudi authorities.
The ministry said one group of suspects was detained close to an oil export terminal and major petrochemical plants in Yanbu, on the Red Sea coast.
The authorities said another alleged cell, which included Africans, was broken up in eastern Saudi Arabia after trying to gather information about oil facilities.
The oil-rich kingdom - the birthplace of al-Qaeda leader Osama bin Laden - has been waging a crackdown on militants since a 2003 wave of attacks on foreign compounds.