Demonstrations erupted across Syria on Friday in response to opposition groups' call for protests about casualties among children during in recent weeks of the uprising against President Bashar al-Assad.

Reuters news agency reported Syrian troops were firing on protesters in the eastern city of Deir al-Zor as rallies continue nationwide in defiance of a government order against gatherings.

Opposition organizers say at least 25 children have died in the recent violence, which has killed about 1,000 people.

Among the young victims is a 13-year-old boy who activists say was tortured and killed by security forces. Syrian authorities say unspecified arfmed groups killed the boy, not government forces.

Syrian opposition figures wrapped up a two-day meeting in Turkey Thursday with a call for President Assad's immediate resignation. They said they are committed to do whatever is necessary to “bring down” Mr. Assad's regime and begin the process of holding new elections to end autocratic rule.

The 300 delegates issued the call in a joint declaration as Syrian forces continued to pound the central town of Rastan, killing at least 15 people, according to activists.

Witnesses say a number of buildings in Rastan have been destroyed. On Wednesday, rights groups put the civilian death toll in that part of Syria at 41 or more, including two young girls.

In Washington, U.S. Secretary of State Hillary Clinton said Thursday that the legitimacy of President Assad's government has “nearly run out,” but that the international community is not yet united on how to deal with the Syrian government's violent tactics.

U.S. officials say they are in contact with the Syrian opposition.

Separately, the U.N. secretary-general's special advisers on genocide prevention expressed grave concern over the loss of life in Syria. They said Thursday they are particularly alarmed by reports that security forces deliberately attacked unarmed civilians.