DARAA, Syria — New violence in a restive southern Syrian city killed as many as six people early today, making it the deadliest single day since anti-government protests inspired by uprisings across the Arab world reached this country last week, an activist said.

The activist said six people died in Daraa when security forces launched an attack near the al-Omari mosque, where anti-government demonstrators have taken shelter.

The violence in Daraa is remarkable in a country like Syria, where security is tightly controlled and state allegiance is expected. So far, the protests have been confined to Daraa and a few surrounding areas — as well as small protests in the capital — but that could rapidly change, particularly if the violence continues.

Groups on social networking sites have called for massive demonstrations across the country Friday, dubbed “Dignity Friday.”

Syria’s state-run TV reported that four people died when “an armed gang” attacked an ambulance in Daraa. It showed footage of guns, hand grenades and other ammunition as well as stashes of Syrian money which it said was seized from inside al-Omari mosque.

The conflicting information and the discrepancy in the toll of the dead could not be immediately reconciled.

The latest attack is likely to raise tension in Daraa as security forces are now expected to intensify their crackdown on anti-government activists.

The Syrian government has sought to contain the first serious intrusion of the Arab world’s political unrest by firing the governor of the southern province of Daraa, where security forces killed seven protesters over the weekend. But the dismissal failed to quell popular anger and the protests reached Nawa, where hundreds of people marched demanding reforms.

Syria, a predominantly Sunni country ruled by minority Alawites, had been spared the wave of uprisings in the Middle East until now.