More than 200 al-Qaida-linked suspects belonging to different cells and involved in different plots against Saudi Arabia have been arrested in recent months.
The Saudi Interior Ministry, in a statement distributed to media, listed six separate arrests but gave no timeline on when the groups were taken into custody.
The total number of the arrested was 208.
The kingdom, which is the birth place of al-Qaida leader Osama bin Laden, has been waging a heavy crackdown on al-Qaida militants since a 2003 wave of attacks on foreigners here. On occasion, it has publicized spectacular arrests, including of terror suspects allegedly targeting its oil wealth.
But Wednesday's announcement by the country that holds a quarter of the world's proven oil reserves indicated that Islamists and al-Qaida were persistent in attempts to rebuild their footholds and networks across the kingdom.
First on the interior ministry's list was the arrest of a group of eight al-Qaida-linked suspects who allegedly planned to attack oil installations. The ministry statement, carried by the Saudi Press Agency, said the eight were part of a terrorist cell led by a non-Saudi man, who was among the arrested.
The planned attacks were to take place in the eastern region of the country, which is home to Saudi's main oil resources. The arrest "pre-empted an imminent attack on an oil installation," the ministry said without naming the target or providing details.
The ministry said 22 other suspects were arrested for allegedly supporting al-Qaida and plotting to assassinate the country's religious leaders and security officials.
Eighteen others, led by an alleged non-Saudi expert in launching missiles, were arrested separately.
"They were planning to smuggle eight missiles into the kingdom to carry out terrorist operations," the statement said of that group.
Also, 112 other Saudis were taken into custody for links and "coordination with outside circles" to assist in smuggling men to troubled areas - shorthand for Iraq and Afghanistan - for training, after which the men would be brought back for attacks in the kingdom, the ministry added.
Thirty-two more men were arrested, both Saudi and non-Saudi, for providing financial aid to al-Qaida operations here, the ministry statement said.
Sixteen men were also arrested in the holy city of Medina, for colluding there to issue a publication propagating "misleading ideology" and criminal acts, the ministry said. The group also worked on helping volunteers go fight in Afghanistan and Iraq.
The statement said security authorities seized a "large quantity of (terror) material" in the sweep but declined to elaborate, saying the ongoing investigation may unveil others linked to the groups.
In February 2006, two suicide bombers attacked the oil facility at Abqaiq on the east coast, killing two security guards and wounding eight foreign workers in an incident later claimed by the Saudi branch of al-Qaida.
The largest previous sweep by Saudi authorities was announced in April, netting 172 militants, including pilots they say were trained for oil refinery attacks using civilian planes.
In August, Saudi Arabia said it was setting up a 35,000-strong special force to protect its oil facilities due to increasing al-Qaida threats.
In early October, Saudi's top religious leader Sheik Abdel-Aziz bin Abdullah al-Sheik, issued a fatwa - or a religious edict - prohibiting sending people to Iraq to take part in the anti-American insurgency there in the name of Islamic jihad, or holy war. The grand mufti warned the young not to be misled by foreign elements who wanted to gain political ambition at the expense of religion.
Wednesday's statement called on all those who were misled and sent to Iraq and Afghanistan to give themselves up to security authorities or to any Saudi diplomatic mission outside the kingdom, and promised their cases would be looked into fairly.
The Saudi announcement came less than three weeks before the biggest Muslim event, the Hajj, when more than two million Muslim pilgrims travel to Saudi Arabia each year and when Saudi steps up security and terror alerts.