ABU DHABI Ñ Saudi Arabia employed helicopters, combat vehicles and a massive ground force to quell nationwide democracy protests.

Saudi opposition sources said National Guard and Interior Ministry troops responded quickly to protest gatherings in major Saudi cities on Thursday. The sources said Saudi anti-riot police, armed with water cannons, quickly dispersed demonstrators, arrested suspected organizers and in some cases engaged in shootouts with armed insurgents.

About 800 people were held or arrested in demonstrations in Jedda and Riyad, the sources said, while smaller protests were reported in Hail and Tabouk. The protest campaign was called by the London-based Movement for Islamic Reform in Saudi Arabia, headed by Saad Al Faqih, Middle East Newsline reported.

Saudi officials said most of the protests were dispersed peacefully. They said two men were arrested in Jedda after they fired into the air outside a mosque meant to serve as a gathering site for an illegal protest.

"Two people fired their handguns in the air near a police patrol vehicle," Interior Ministry spokesman Brig. Gen. Mansour Turki said. "They were arrested straight away, but there was no exchange of fire and no one was hurt."

Saudi authorities closed parts of Riyad and Jedda to prevent people from arriving at the demonstrations. Helicopters flew overhead to search for protest gatherings.

This was the second time in as many months that Saudi authorities foiled plans for nationwide protests. In November, the Movement for Islamic Reform in Saudi Arabia failed to organize protests amid a rapid response by authorities.

On late Wednesday, more than 30 Saudi pro-government clerics called for Saudis not to participate in demonstrations.

At the same time, Osama Bin Laden was said to have called for the overthrow of the Saudi regime. In an audiotape posted on an Islamic website, Bin Laden called the royal family sinful and corrupt.

"The sins the regime committed are great," the message said. "It practiced injustices against the people, violating their rights, humiliating their pride."