Syrian opposition activists say more than 90 people have been killed in fighting between government forces and rebels in Homs province.
They say 13 children are among the dead and 100 people were wounded as the Syrian army shelled the town of Houla.
Activists report confrontations in other Syrian cities including Damascus, the BBC reports.
They say army tanks were deployed in Aleppo to contain demonstrators after Friday prayers.
In Houla, Syrian forces used tanks, mortars and heavy machine guns, according to both the Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees activist groups.
They had earlier reported at least 50 dead in the shelling.
International media cannot report freely in Syria and it is impossible to verify reports of violence.
Meanwhile, UN chief Ban Ki-moonsaid the opposition controlled significant parts of some cities.
In a letter to the Security Council, Mr Ban said the situation remained extremely serious and urged states not to arm either side in the conflict.
Meanwhile, Al Arabiya television reports a Russian cargo ship loaded with weapons is due to arrive at a Syrian port this weekend.
Western diplomats in New York describe the report as credible.