"Around one thousand protesters gathered in and around the Omari mosque shouting anti-regime slogans, amid a heavy security and army presence," said the activist in Daraa, 100 kilometres (60 miles) south of Damascus.

The demonstrators formed a human shield around the mosque to prevent security forces from approaching it, he added.

An AFP photographer and videographer in Daraa said their car was stopped in the old town and their equipment confiscated.

After being taken in for questioning, they received an apology from the authorities, but had still not received their equipment back.

The photographer said soldiers were manning checkpoints at all entries to the town and were cross-checking the identity cards of travellers with a list of names they had compiled.

The demonstrations also spilled into the nearby towns of Jassem and Noa, where eyewitnesses said more than 2,000 protesters gathered for a rally before being quickly dispersed by security forces.

Syria, which is still under a 1963 emergency law banning demonstrations, has witnessed a string of small but unprecedented protests demanding the end of the ruling Assad regime for one week now.

Daraa, a town that is home to large tribal families, has been the focal point of the rallies, the latest in a string of uprisings against long-running autocratic regimes in the Arab world.

Six people have been killed in a security crackdown on the Daraa demonstrations, including an 11-year-old boy who died after on Monday inhaling tear gas the day before.

Syrian authorities on Tuesday also detained writer Louai Hussein, one day after he posted a petition online demanding the right to freedom of expression, a London-based rights group reported.

"Syrian security forces broke into the home of Louai Hussein on the outskirts of Damascus on Tuesday, and his whereabouts remain unknown," said a statement by the Syrian Observatory for Human Rights.

"He had posted a petition online the day before to demand the right to peaceful protests and freedom of expression," the statement added.

Hussein, 51, is a former political prisoner who was jailed from 1984 to 1991 over his activism with the communist party in Syria, the group said.

Organisations including Human Rights Watch have accused the Syrian authorities of detaining dozens of activists at a rally outside the interior ministry last week.

The crackdown on protesters also earned a harsh rebuke on Tuesday from the European Union, which condemned the authorities' handling of the protests.