(CNN) -- The number of people killed by indiscriminate gunfire from government forces in the western Syrian city of Hama on Friday may exceed 80, said the London-based Syrian Observatory for Human Rights, citing reliable medical sources.
Killings occurred when security personnel opened fire on demonstrators, who took to the streets after Friday prayers, witnesses said.
More than 1,000 people have been killed in Syria since anti-government demonstrations began in mid-March, according to the United Nations. President Bashar al-Assad's regime has undertaken a fierce crackdown against demonstrations that have demanded governmental reforms.
Demonstrations across the country on Friday were dedicated to children who have taken part in the persistent and angry uprising against the Syrian government.
At least 51 children have been killed by security forces since the anti-government protests started in mid-March, the Local Coordination Committees of Syria said. They include Hamza Ali al-Khateeb, the 13-year-old Daraa boy whose killing has captured the world's attention, and a 4-year-old shot in Rastan, a town in restive Homs province.
"Violence against children must stop and children's safety must be upheld at all times," Marta Santos Pais, the U.N. secretary-general's special representative on violence against children, said on Friday.
"Children need to be protected from unlawful arrest, torture and ill-treatment, and their lives should not be put at risk under any circumstance," she stressed.
CNN has not been granted entrance to Syria and cannot independently confirm the latest reporting from the country.
One witness in Hama, a dentist, told CNN he was taking part in the demonstrations when marchers were "surprised" by the military and the shabiha, armed pro-regime elements, opened fire in what he called an "intense" situation.
The witness provided the names of nine slain people, whose bodies were seized by government supporters.
Another witness there reported at least one demonstration in which tens of thousands of people took to the streets.
The witness said people were heading toward a square in the center of town and chanted, "Freedom, freedom! National unity! Christians and Muslims are one! Leave, leave" and, "The people want the fall of the regime."
That same witness later reported small demonstrations in some areas, with protesters burning tires amid intermittent gunfire.
Hama is the scene of a notorious crackdown a few decades ago.
The Baathist government of Hafez al-Assad, who once ruled Syria, crushed a 1982 revolt in Hama against the Sunnis, who are the majority religious group in Syria. Hafez Al-Assad is the late father of Syria's current president, Bashar al-Assad.
Estimates put the death toll then at between 10,000 and 30,000 people; the exact number was never known. The government has been dominated by the al-Assad family's Alawite community, a minority religious group that is an offshoot of Shiite Islam.
U.S. Secretary of State Hillary Clinton said her office was "deeply concerned" with recent reports that Syria's internet services has been shut down.
"We condemn any effort to suppress the Syrian people's exercise of their rights to free expression, assembly, and association," she said in a statement released Saturday.
"We believe that even in the face of significant obstacles, the Syrian people will -- and should -- find a way to make their voices heard," she said.