Justice ministry says convictions on charges including conspiring with Al Qaeda.
Saudi security courts sentenced one person to death and others to prison in the first trials arising from Al-Qaeda's bloody 2003-2006 campaign of attacks inside the kingdom, the justice ministry has said.
Altogether 330 people were tried out of 991 charged in the attacks, with an unspecified number convicted on charges including conspiring with Al-Qaeda, plotting to disrupt national security and financing terrorism, the ministry said in a statement carried by state news agency SPA.
"These charges include membership of a deviant group and involvement in its activities, communicating and coordinating, and working with foreign agencies to conspire against national security by causing mayhem and insecurity," the ministry said.
"Deviant group" is the Saudi government's standard wording for Al-Qaeda.
No details were given about individuals, but the ministry said the convictions came in trials involving 179 cases. Sentences ranged from house arrest to imprisonment and, in one case, the death penalty.
Some defendants were acquitted, the ministry added without providing details.
According to officials, the trials related to a wave of bombings and assassinations launched in early 2003 that left more than 100 expatriates and Saudis dead and stunned the government, which until then had not believed that Al-Qaeda had a significant presence in the country.
The campaign began with spectacular assaults on three upscale compounds housing mostly European and US expatriates in Riyadh on May 12, 2003, killing 35 people and wounding dozens more.
Al-Arabiya television, which is closely linked to the government, said among those tried were suspects from those attacks, the November 8, 2003 bombing of Al-Mohaya compound west of Riyadh, attacks on the interior ministry and other government offices in Riyadh.
Also in the dock were suspects from a failed February 24, 2006 assault on the Abqaiq oil processing centre in eastern Saudi Arabia.
The trials of the militants are believed to have begun early this year but have only now been officially confirmed.
Human rights activists have criticised them for being held in secret and based on poorly defined charges, and said the suspects were denied fundamental rights including legal help in their defence.
Justice ministry spokesman Abdullah al-Saadan said the defendants had been accorded the right to defence lawyers in the special security courts, according to SPA.
"The accused has the right to defend himself as well as to having lawyers to defend him," he said, adding that the verdicts could be appealed.
But Christoph Wilcke of the New York-based group Human Rights Watch said on Wednesday that according to his information, including contacts with some accused and their families, those tried did not have legal representation and Saudi rights groups did not attend the trials, despite pledges to the contrary.
He also questioned how the hearings took place, saying that many of the accused were tried in groups defined by the incident they were accused of taking part in.
"My very limited sources indicate the trials were summary in nature, and while I cannot verify that, it's cause enough for concern because of the closed nature of the trials," he told AFP.
Wilcke also said it was to the Saudis' credit that the suspects were put on trial after waiting for years in prison.
Abdullah said that others facing similar charges would be tried "in due course,", according to SPA, and that arrangements were being made to permit media coverage.
According to Washington-based Saudi security researcher Christopher Boucek, the Saudis hold around 4,000 people arrested in security-related cases in prison, both charged and uncharged.