Police in Saudi Arabia have arrested at least 50 people who tried to demonstrate for reform and the release of political prisoners. A London-based Saudi opposition group called for demonstrations in nine cities, but police prevented most of them.

The most successful protest was in the port city of Jeddah, where about 100 people tried to demonstrate. About half of them were arrested. Police were out in force to prevent the protests and most of the marches did not even get started, as a result.

But reports from Jeddah say about 100 people managed to hold a brief demonstration before police moved in.

The London-based group, Movement for Islamic Reform, in Arabia had called for protests throughout Saudi Arabia, using radio broadcasts and an Internet website to promote the plan.

The U.S. embassy in Riyadh listed the locations on its website, and urged Americans to avoid the areas in case there was trouble.

The same opposition group called for a protest last week in Riyadh, at which at least 270 people were arrested. The government says 83 are still in custody and will be prosecuted. At that rally, hundreds of mostly young Saudis disregarded the country's ban on demonstrations, and called on the government to implement drastic reforms.

Saudi Interior Minister, Prince Nayef, warned on Wednesday that the government would punish anyone caught participating in any new demonstrations.

Saudi Arabia has been cracking down on suspected Muslim militants. But some critics say granting more civil liberties would be the best way to fight the growth of extremism in the kingdom.

At Cairo University, former Egyptian diplomat and political science professor Abdullah AlAshaal, who has written extensively about the Persian Gulf region, says there is an awareness now among Saudi leaders that reforms are necessary.

"The leadership is aware that their tradition should be changed, and the relationship between them and the population should be different," he said. "The population is changing while the signals of the change are not counted by the leadership."

Mr. AlAshaal says that new awareness was behind the announcement last week that Saudi Arabia will hold its first municipal elections sometime in the future.

As it is now, Saudi Arabia's royal family has absolute power. Saudi citizens cannot hold public meetings to discuss political or social issues, and press freedoms are greatly limited.