Syrian forces killed 12 protesters overnight in the central city of Homs in clashes after the death of a tribal leader in custody, a rights campaigner in Homs said on Monday.

"Homs is boiling. Security forces and the regime thugs have been provoking armed tribes for a month now. But civilians in large numbers also took to the streets in different areas of Homs last night and they were shot at in cold blood," the rights campaigner told Reuters.

The violence comes shortly after Syrian security forces killed three mourners on a highway outside the town of Talbiseh, slightly north of Homs, on Sunday when they opened fire on a funeral that had turned into a demonstration, two witnesses said.

They had been attending the funeral of a man killed the day before by security forces, the witnesses said. The mourners marched across a bridge on the highway near where security police and gunmen loyal to President Bashar Assad were stationed.

Despite Assad's promises of reform such as lifting the decades-old emergency laws, protests continued to erupt in several cities in Syria with thousands of people taking to the streets to call for greater freedom.

Thousands of protesters in the southern town of Suweida participated in a rally to mark Evacuation Day, commemorating the departure of the last French soldiers 65 years ago and Syria's proclamation of independence.

Supporters of Assad were present alongside protesters, declaring loyalty to the president.

Several hundred people chanted "the people want freedom" at the grave of independence leader Ibrahim Hananu in Syria's second city Aleppo on Sunday, a rights campaigner in contact with the protesters said.

Aleppo, a large trading and industrial hub, has been mostly free of protests since mass pro-democracy demonstrations challenging President Bashar al-Assad's authoritarian rule erupted more than a month ago in southern Syria and spread to large parts in the country of 20 million people.

Assad said on Saturday that the emergency laws, in place for almost 50 years, would be lifted by next week. But he did not address protesters' demands to curb Syria's pervasive security apparatus and dismantle its authoritarian system.

"God, Syria, freedom, that's all," chanted several hundred protesters in the South Syria town of Suweida. They also shouted "no fear" and slogans in support of the city of Deraa, where protests first broke out a month ago and has suffered the heaviest bloodshed.

Human rights groups say more than 200 people have been killed since demonstrations erupted in Deraa on March 18 in protest against the arrest of youths who had scrawled graffiti inspired by the Arab uprisings in North Africa.