Syrian forces fired tear gas and live ammunition to disperse thousands of protesters calling for the removal of President Bashar al-Assad, reportedly killing two people in the northern city of Aleppo, opposition groups have said.
Crackdowns on protests, such as Friday's violence in Aleppo and other cities, are routine despite the deployment of more than 250 UN observers who have fanned out around Syria to monitor a ceasefire brokered by international envoy by Kofi Annan.
Despite the daily violations, UN Secretary-General Ban Ki-moon said on Thursday that there was no "plan B" for the Annan initiative.
Friday's violence during weekly anti-government protests was reported by the Britain-based Syrian Observatory for Human Rights, which has a network of activists on the ground, and by the opposition Local Coordination Committees.
The Observatory said one person was killed and another wounded in Aleppo, a major economic hub which has remained largely supportive of Assad throughout the uprising but where anti-regime sentiment has been on the rise in recent weeks.
Aleppo-based activist Mohammad Saeed said one of the protesters later died of his wounds, raising the number of those killed in the city's Boustan al-Qasr district to two.
He said more than 10,000 people were protesting in the city.
"The regime is desperately trying to put down the protests in Aleppo but all this violence will backfire," he said.
Amateur videos posted online by activists showed several wounded people, including a teenage girl, being carried away by other protesters.
The Observatory said a boy was also killed by snipers fire in the Damascus suburb of Arbeen ahead of a protest there.
In northwestern Idlib province, tens of thousands of people marched in the rebel-held localities of Maaret al-Numan, Saraqe, Kafrnoubol, Hass and Sarge, said Rami Abdel Rahman, the head of the Observatory.
Clashes reportedly pitted regime forces against army deserters in the Idlib village of Maarshurin.
In the southern town of Inkhel, several people were wounded when troops opened fire at protesters, while in the central Homs region, seven people were reported wounded as a result of security forces' gunfire.
In the capital Damascus, troops fired tear gas to disperse a large demonstration that started as protesters emerged from the Daqaq Mosque in the restive Midan district in Damascus.
Earlier, government forces shelled the Qusour and Jobar neighborhoods in the city of Homs, but there was no immediate word on casualties.
The UN estimated in March that more than 9,000 people have been killed in the revolt against Assad, which began in March 2011 as a largely peaceful protest movement calling for reforms but has since morphed into an insurgency. The death toll rises every day.
The UN's Ban said on Thursday that Annan's peace plan is the only option right now for ending the violence in Syria.
The former UN secretary-general's plan calls for a complete cessation of violence but Ban said "unfortunately, this has not been implemented".
He said the deployment of UN observers to Syria has had "some dampening effect" but the violence hasn't stopped.
Ban said this requires "strong political will" by Syrian President Bashar Assad and full cooperation by opposition forces.
Ban said he spoke Wednesday to Annan, who said he will be going to Syria soon but no date has been fixed.