Syrian security forces shot dead at least 10 people overnight in a central city where dozens have been reported killed since the weekend, activists and witnesses said.

Mohammed Saleh, a resident of Homs, said smoke was billowing over the city after a night of intense gunfire.

The death toll was confirmed by Syrian rights activist Mustafa Osso and the Local Coordinating Committees, which organize and track the protests. Damascus-based Abdul-Karim Rihawi, head of the Syrian Human Rights League, also said there were casualties in Homs but he did not have an exact figure.

Syria has been trying to crush a four-month-old uprising that has posed the gravest challenge to the 40-year ruling dynasty of the Assad family.

Human rights groups say more than 1,600 people, most of them unarmed civilians, have been killed in President Bashar Assad's crackdown on a largely peaceful protest movement. The government disputes that toll and blames the unrest on gunmen and religious extremists looking to stir up sectarian strife.

The Syrian Observatory for Human Rights and Saleh, the activist in Homs, said a wave of sectarian fighting killed up to 30 people there over the weekend. Both said they have the names of the victims.

Witnesses said the violence began Saturday after the corpses of three Alawite government supporters were dumped in Homs with their eyes gouged, prompting revenge attacks by pro-government militias.

But other activists said the toll was lower and blamed security forces for the killings.

The opposition accused Assad's minority Alawite sect of trying to stir up trouble with the Sunni majority to blunt the growing enthusiasm for the uprising. The protesters have been careful to portray their movement as free of any sectarian overtones.

Syria has banned independent media coverage, making it difficult to confirm accounts from the ground.

The pro-government daily Al-Watan blamed the violence in Homs on terrorists and said the army was deploying there.

Saleh, the Homs-based activist, said there was intense shooting all through the night until Tuesday morning in some areas of Homs. He saw smoke billowing from the area amid cracks of gunfire.

"People who don't have important work to do are staying at home," Saleh said.