Supporters of Sheikh Wahid al-Balous, who was the leader of a powerful Druze militia, blamed the regime for twin car bombings in the southwestern city of Sweida that killed him and 27 other people, the Syrian Observatory for Human Rights said.
"Six members of regime security forces were shot dead last night during demonstrations in Sweida," Observatory chief Rami Abdel Rahman said.
Balous was a popular figure among Syria's Druze minority which made up around three per cent of the country's pre-war population of 23 million.
But he also opposed conscription of Druze men in a province where thousands of the sect's members have evaded service in the Syrian army's dwindling ranks, refusing to take up arms outside their own areas.
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As word of Balous's death spread last night, protesters pelted the municipality building with stones, and gunfire was heard outside two security headquarters in the city.
Residents said demonstrators also smashed a statue in the city centre of Hafez al-Assad, father and predecessor of President Bashar al-Assad.
Today, calm returned to the city although residents said internet connections remained down and an army checkpoint blocked the main road to Damascus.
In the capital, a security source insisted the demonstrations were against "terrorism" not the regime.
State media reported the car bombs but made no mention of Balous's death.
Sweida has largely been spared the violence that the rest of Syria has experienced since the conflict erupted in March 2011.
But there has been occasional unrest, including a protests days before the bomb attack by residents demanding more better government services, including power and water.