Hundreds of Syrians have staged a rare protest in the capital, Damascus, calling for democratic reforms and the release of all political prisoners.
Six protesters were reportedly detained by the security forces, a witness told the BBC Arabic Service.
The AP news agency said government supporters later broke up the rally by punching and attacking the protesters.
A Facebook group, The Syrian revolution against [President] Bashar al-Assad 2011, is said to have called the march.
A similar appeal on Facebook last month failed to bring protesters to the streets, but critics blamed a heavy security presence for the failure of that campaign.
Calls for reform
Tuesday's march started after noon prayers in the old town of Damascus and fanned out to neighbouring streets, the witness told the BBC.
He said the security forces did not use force against the protesters, but detained six of them. He added that more people were expected to join demonstrations after the evening prayers.
A video posted on YouTube appeared to show the protest, with hundreds of marchers chanting slogans calling for freedom and an end to the emergency laws.
Calls for protests in Syria surfaced on Facebook after Egyptian activists succeeded in overthrowing President Hosni Mubarak last month after weeks of street demonstrations.
Syria - like Egypt - is ruled through emergency law and suffers from high poverty and unemployment. Critics say corruption and cronyism are rife in Syrian business and political circles.
President Bashar al-Assad - who came to power in 2000 after three decades of rule by his father Hafez - has moved slowly to open up the economy, but his administration does not tolerate any dissent.
There are thousands of political prisoners in Syrian jails, and major opposition groups are banned. The government also blocks access to several internet sites and maintains strict control of the media.
In January, President Assad told the Wall Street Journal that Syria was more stable than Tunisia and Egypt. He said that there was no chance of political upheaval, and pledged to press on with a package of reforms.