Syrian security forces opened fire at a funeral procession Tuesday, killing at least 10 people in a city that has been besieged for days by some of the most serious violence seen during the country's four-month-old uprising, activists said.

Tuesday's killings bring the death toll in Homs to about 50 people since Saturday, according to a range of activists, human rights groups and witnesses. Syria has banned independent media coverage, making it difficult to accounts from witnesses or Syrian authorities.

"We haven't slept since yesterday," a Homs resident told The Associated Press by telephone, the cracks of heavy machine-gun fire in the background. "I am laying down on the floor as I talk to you. Other people are hiding in bathrooms."

He described Homs as a "ghost city," with most people holed up inside their homes.

He asked that has named not be published for fear of reprisals from the government.

The shooting outside the Khaled bin Al-Waleed mosque erupted shortly after noon as families held funeral processions for 10 people killed a day before during a security sweep, said the Local Coordination Committees, which help organize and track the protests in Syria.

A mother of one of the men being buried was believed to be among the victims.

Syrian troops have been conducting operations in Homs since late Monday following reports of a wave of sectarian killings that left some 30 people dead over the weekend.

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.