The toll from twin car bombs that rocked the outskirts of the Syrian city of Sweida Friday has risen to 26 people, including a prominent Druze cleric known for criticising Syria's regime, a monitor said.

"The death toll from the car bomb attacks outside Sweida has risen to 26 people. Another 50 people are wounded," said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.

Abdel Rahman earlier said that Sheikh Wahid al-Balous, who spoke out often against both the Syrian regime and Islamists, was killed in the attack as he was driving on the outskirts of the city.

The second car bomb struck near the hospital in the Dahr al-Jabal neighbourhood where the wounded were being taken, the monitor added.

Syria's official news agency SANA earlier said eight people had been killed and 22 wounded.

Sweida is the heartland of Syria's Druze minority, which made up around three percent of the country's pre-war population of 23 million.

"Balous was the leader of the Sheikhs of Dignity group, which aimed to protect the Druze areas in Syria," said Malek Abu Kheir, a journalist from Sweida who knew him.

The Sheikhs of Dignity are the most powerful militia in the area and had fought fierce battles against the Islamic State jihadist group and Al-Qaeda's Syrian affiliate.

Balous opposed army conscripts from Sweida being sent outside the province, and often spoke out against both jihadist groups and the regime of President Bashar al-Assad, Abu Kheir told AFP.

Days before Balous was killed, Sweida residents had gathered in the city to demand more regular government services, including electricity and water.

Activists told AFP the protesters had the support of Balous.

The head of Lebanon's Druze community Walid Jumblatt, in a condolence statement he posted on Twitter, accused the Assad government of killing Balous.

"My condolences to Sheikh Wahid al-Balous and his companions, who were assassinated by the regime of Bashar al-Assad," he said.

But the chief of Syria's Druze, Sheikh Youssef Jarboua, accused "the enemies of the nation and humanitarian state".

Syrian Information Minister Omran Zohbi said the "terrorism that struck Sweida wants to send a message to its people, that because they stood by their nation, they will pay the price of this stance with blood".

According to SANA, parliament condemned "the two terrorist explosions in Sweida".

"These cowardly terrorist acts will not discourage the Syrian people from continuing their fight against terrorism, but will instead strengthen their perseverance," the parliament statement said.

Neither Zohbi nor the parliamentary statement mentioned Balous.

The Druze community has been somewhat divided during the war, with some members fighting on the government side and others expressing sympathy for the opposition.

Thousands of Druze men have evaded military service in the army's dwindling ranks and have mostly taken up arms only in defence of their own areas.

In Sweida, Druze have formed a local militia to protect themselves from the rebels, residents say.