|Syrian children carry pictures of 13-year-old Hamza al-Khatib and hold candles during a protest [Reuters]
Syrian activists have called for protests on Friday over the dozens of children killed in anti-government protests, as the opposition continues to demand the "immediate resignation" of Bashar al-Assad, the country's president.
Rejecting government concessions, opposition groups at a meeting in Turkey called late on Thursday for parliamentary and presidential elections within a year of Assad's removal and vowed to work "to bring down the regime".
Hillary Clinton, the US secretary of state, said the international community needs to be more united on dealing with the Syria government's crackdown on the pro-democracy movement.
"Right now the attitude of the international community is not as united as we are seeking to make it," she said in Washington, apparently alluding to Russia's moves blocking a proposed UN Security Council condemnation of Syria.
Activists called for "Children's Friday" protests to honour the children killed in the uprising, such as 13-year-old Hamza al-Khatib whom activists say was tortured to death, a charge denied by the authorities.
"The people want the fall of the regime. Tomorrow, it's 'Children's Friday' of rising up against injustice, like the adults," the activists announced on their Facebook page "Syrian Revolution 2011", an engine of the revolt.
The UN children's agency UNICEF says at least 30 children have been shot dead in the revolt against Assad's autocratic rule which erupted in mid-March.
The more than 10-week-old revolt in Syria was sparked by the arrest and torture of 15 children and adolescents accused of painting anti-regime graffiti in the southern town of Daraa, which became a flashpoint of the deadly protests.
"A photo of a child who is dead or being tortured or being mutilated is much more powerful than of an adult," Patrick McCormick, UNICEF spokesman, said, referring to the Facebook campaign focused on the fate of Hamza.
"The use of Facebook or any image especially of children is incredibly powerful," he told AFP news agency. "They are innocent victims here, they get caught in the middle, it is not their fight."
McCormick said the situation would worsen with the end of the academic year. "It will leave the children and teenagers more vulnerable because they will be out and about and not sitting in a classroom."
On the ground, security forces armed with heavy machine guns shot dead 15 civilians in Rastan on Thursday, a human-rights activist said, adding to a toll of at least 43 killed in towns of the flashpoint Homs region since Sunday.
The UN chief's special advisers on prevention of genocide and responsibility to protect civilian populations expressed alarm on Thursday at the mounting death toll in Syria.
"We are particularly alarmed at the apparently systematic and deliberate attacks by police, military, and other security forces against unarmed civilians," Francis Deng and Edward Luck, the advisers to Ban Ki-moon, said.
More than 1,100 civilians have been killed and at least 10,000 arrested in a crackdown on near-daily anti-government demonstrations since March 15, human rights organisations have said.
The Syrian government insists the unrest is the work of "armed terrorist gangs" backed by Islamists and foreign agitators.