Security forces were said to have used tear gas and gunfire in and around the capital, Damascus, with unconfirmed reports of casualties.

Meanwhile, the EU has expanded sanctions against the Assad regime.

It added three members of Iran's Revolutionary Guard and four Syrians to a list of more than 30 people targeted.

The EU's official journal said the three Revolutionary Guard members now subject to sanctions had been "providing equipment and support to help the Syrian regime suppress protests in Syria".

The EU also drafted a declaration condemning the "unacceptable and shocking violence the Syrian regime continues to apply on its own citizens".

EU leaders are expected to endorse the declaration later.

More than 1,300 people have been killed and thousands more detained since a crackdown on anti-government protests began in March, activists say.

As in previous weeks, activists appealed to Syrians to join demonstrations after Friday prayers.

An appeal on Facebook listed a slogan for this week as: "Bashar is no longer my president and his government no longer represents me."

Thousands of people were reported to have turned out in the Damascus suburb of Irbin, the central cities of Homs and Hama, Deraa in the south, and Qamishli and Deir al-Zour in the east.

Residents in Homs told BBC Arabic that one person had been killed in a protest in the district of Jawret al-Arayeis.

The London-based Syrian Observatory for Human Rights said one person had been killed and nine injured in Kiswah, south of Damascus.

Syria has prevented most foreign journalists from entering the country and reports of unrest are hard to verify.

The Local Coordination Committees, which monitor the Syrian protest movement, had earlier reported military trucks in Damascus suburbs, and said roads in the centre of Homs had been blocked.

Friday's protests come after President Assad offered dialogue and reform on Monday, in his third address to the nation since the start of demonstrations.

Activists dismissed the offers as cosmetic or insufficient, and clashes broke out between supporters of President Assad and anti-government protesters on Tuesday.

In the north, Syrian residents have been continuing to flee a widening crackdown by the army.

Turkish state media said more than 1,500 people had crossed the border from Syria on Thursday after troops and tanks moved into the Syrian border village of Khirbet al-Jouz.

Residents and journalists in the Turkish village Guvecci said they could see military activity across the border.

Activists from the Local Coordinating Committees said snipers were also spotted on roofs.

A total of 11,700 Syrian have sought refuge in Turkey, the Turkish government says.

US Secretary of State Hillary Clinton said the reported Syrian troop movements were "very worrisome".

The Iranians added to the EU sanctions list were two Revolutionary Guard commanders, Maj Gen Qasem Soleimani and Brig Cmdr Mohammad Ali Jafari, and the Guard's deputy commander for intelligence, Hossein Taeb.

They will now be subject to having their assets frozen and being banned from travel.

EU officials did not give details of the equipment or support they were accused of providing to Syria.