Syrian security forces have dispersed thousands of protesters marching towards central Damascus from the suburb of Douma, witnesses say.

Haitham al-Maleh, an activist and lawyer, told Al Jazeera on Friday that protesters were close to Abasyeen Square when the intelligence services brought several buses carrying men with "pistols and sticks" who attacked protesters. He said those injured were taken away by medics.

Other sources said security forces used tear gas to disperse the crowds.

"I counted 15 mukhabarat [secret police] busloads. They went into the alleyways just north of the square chasing protesters and yelling 'you pimps, you infiltrators, you want freedom? we will give it to you'," a witness told Reuters news agency.

Elsewhere in the capital, violence reportedly erupted when dozens of armed men in plain clothes surrounded about 250 protesters rallying in front of the Salam mosque in Barzeh district.

Thousands were also demonstrating in the southern city of Daraa.

Al Jazeera's Rula Amin reported earlier in the day that security forces were not visible in the city, and that the protesters were being allowed to hold their demonstration.

"It's a completely different scene from last Friday when more than 26 people were killed during protests and clashes with the security forces and protesters here. Today, no security forces are visible at all. People went out after Friday prayers ... in thousands. They were marching carrying olive branches saying 'peaceful, freedom'. Some were demanding the toppling of the regime, others were saying they just want reforms," she reported.