Hundreds of security forces made a show of force in two Saudi cities Thursday to ward off any protests against the royal family, chasing a few would-be demonstrators in the streets and arresting several others, after a dissident called for a day of marches.

The London-based dissident Saad al-Fagih (search), head of the Movement for Islamic Reform in Arabia (search), had predicted "tens of thousands" of demonstrators would turn out in the capital, Riyadh, and the port city of Jiddah.

Such numbers did not show up, but the threatened show of defiance to the kingdom's ban on protests caused the government to deploy large numbers of security forces, checkpoints and helicopters.

Several men and women were reported arrested in both cities, but officials wound not confirm or deny the reports.

Several hours after the protests were supposed to begin, the assembly area for the Riyadh protest bristled with police and special forces — but no demonstrators. Helicopters circled overhead and police checkpoints stopped motorists.

Policemen were seen frisking a man lying on the ground before placing him in a police car.

Interior Ministry spokesman Brig. Gen. Mansour al-Turki said two men were arrested in Jiddah after firing a pistol in the air, and a security official speaking on condition of anonymity said they might be connected to al-Fagih.

During the day, al-Fagih's group told reporters the assembly point had changed to two other locations. But reporters who went to the locations found normal pedestrian traffic and no police.

In Jiddah, at least six people were seen being arrested and dozens in small groups were seen running from police. At one point, a volley of gunshots could be heard in an area where protesters were trying to gather. It was not immediately clear what happened.

Al-Fagih had called the protests via his satellite television and radio stations and Web site. In the group's boldest challenge to the monarchy, its Web site spelled out "immediate procedures to be taken after the demise of Al Saud" royal family.

The royal family will leave behind "a massive legacy of poverty, unemployment, crime, ailing infrastructure, and scores of prisoners, tortured ones and a social chaos," the Web statement said, calling on security officers to retain their positions to prevent chaos after the monarchy's downfall.

Al-Fagih could not be reached Thursday. His London telephone was continuously engaged.

In the northwestern city of Tabuk, a few people demonstrated outside government buildings, witnesses said, and similar gatherings were reported in Hail. No confrontations with the police occurred, the witnesses said.

Al-Fagih's group says it seeks to replace the monarchy with a liberal, democratic government. In today's Saudi Arabia, the king wields absolute power. There are no legal political parties. Public protests are banned and the press is controlled.

The Saudi government accuses al-Fagih of extremism and says he has strong ties to terrorists, a charge al-Fagih denies.

Many reform-minded Saudis question al-Fagih's motives and liberal credentials, saying he has no clear reform plan.

Turki al-Hamad, a respected columnist and former political science professor, said that on his radio and TV programs, al-Fagih constantly attacks liberals as nonbelievers and enemies of Islam.

"So how can he call himself a reformist?" said al-Hamad.

However, al-Fagih's criticism of the royal family strikes a chord among some lower-income Saudis, who claim the royal family does not distribute the kingdom's oil-wealth equitably.

The same day the protests were called, an audiotape attributed to another Saudi dissident, Usama bin Laden (search), appeared on a Web site known for militant Islamic postings. The tape fiercely criticized the Saudi royal family.

The Saudi monarchy has grappled with conflicting pressures in the past two years from militant Islamists, who have staged suicide bombings and kidnappings of foreigners, and from the United States, which has called for liberal reform. Saudi intellectuals, too, have urged reform, arguing that the country's strict interpretation of Islam has yielded a society that is conducive to extremism.

The government has promised municipal elections next year, the first of any kind in the kingdom in years, and recently launched a national dialogue to open public debate on democratization and other issues.

Al-Fagih failed to pull off simultaneous large-scale protests in nine Saudi cities last year. Only about 100 protesters in Riyadh and similar numbers in Jiddah, Dammam and Hail showed up.