Syrian opposition figures have wrapped up a two-day meeting in Turkey with a call for President Bashar al-Assad's immediate resignation.

The 300 delegates issued the call in a joint declaration on Thursday, as Syrian forces continued to pound the central town of Rastan. Activists say at least 15 people were killed Thursday in the government's shelling.

The opposition figures in Turkey say they are committed to do whatever is necessary to “bring down” Mr. Assad's regime and begin the process of holding new elections and end 11 years of autocratic rule.

As they met in the Turkish town of Antalya, a small group of Syrian government supporters rallied nearby, vowing their allegiance to Mr. Assad.

Earlier Wednesday, witnesses say a number of buildings in Rastan had been destroyed as the government continues its crackdown. On Wednesday, rights groups put the civilian death toll in that part of Syria at 41 or more, including two young girls.

Syrian activists say at least 25 children are among the more than 1,000 people killed, overall, during the uprising against President Assad.

Opposition organizers say that demonstrations they have called for Friday will honor the children killed in the uprising, among them a 13-year-old boy who activists say was tortured and killed by security forces – a charge denied by Syrian authorities.

U.S. Secretary of State Hillary Clinton says the legitimacy of President Assad's government has “nearly run out.” However, she says the international community is not united enough on how to deal with Syria's crackdown on opposition protests. Her comments came Thursday in Washington.

Separately, the United Nation's special advisers on genocide prevention have expressed “grave concern” over the loss of life in Syria. In a Thursday statement, they said they are “particularly alarmed” by the apparent attacks by security forces against unarmed civilians.

Witness reports of casualties in Syria, as well as official accounts, are difficult to independently verify because the government has barred most international journalists from the country.

On Wednesday, the government freed hundreds of political prisoners after Mr. Assad announced a general amnesty. The releases were an apparent bid to appease activists calling for his resignation. The United States and France both said the amnesty would not be enough.

Also Wednesday, President Assad announced the formation of a committee to map out a national dialogue with the opposition.