© ReutersDemonstrators protesting against Syria's President Bashar al-Assad march through the streets after Friday prayers in Hula, near Homs October 28, 2011. Picture taken October 28, 2011.
Syrian tanks pounded an old district in the city of Homs on Saturday and three people were killed, activists said, after one of the bloodiest days of the seven-month-old uprising against President Bashar al-Assad.
Activists and residents said Syrian forces shot dead 40 civilians on Friday when they fired on demonstrators calling for international protection from Assad's crackdown.
The Arab League and United Nations condemned the violence.
U.N. Secretary-General Ban Ki-moon said Assad must respond to demands for change with serious reform, "not repression and violence," and called for an immediate halt to military operations, his spokesman said.
One activist group said fierce fighting broke out in Homs on Friday night between dozens of army deserters and forces loyal to Assad. Seventeen soldiers were killed when the defectors attacked two security posts in the city, it said.
The report by the British-based Syrian Organization for Human Rights highlights the emerging element of armed insurgency alongside mainly peaceful street protests demanding an end to 41 years of Assad family rule.
The United Nations says 3,000 people, including nearly 200 children, have been killed in the unrest. Since the start of protests in March, Syrian authorities have blamed the violence on gunmen they say have killed 1,100 soldiers and police.