Hisham Sha'ar, who heads the Syrian supreme committee for presidential elections, said recently that Syrians left the country illegally can't cast their ballots.

Government officials say President Bashar al-Assad is the "real guarantee" for the future of Syria and that it is very likely that he will be re-elected for a third seven-year term.

Violence persisted in the run-up to the presidential race.

On Thursday, a child was killed and 22 others wounded when mortar shells hit the pro-government suburb of Jaramana, east of the capital Damascus.

Mortar attacks on Jaramana have become almost a daily occurrence as the area is adjacent to the rebel-held al-Mlaiha suburb, where intense battles are currently taking place between rebels and government troops trying to wrest control over the strategic area.

SANA, the state news agency, said government troops on Thursday advanced in Damascus' eastern suburb of Jobar, killing an undisclosed number of rebel fighters.

On the opposition side, the Britain-based Syrian Observatory for Human Rights said government air strikes hit a school on Wednesday in a rebel-held area in Syria's northwestern province of Aleppo, killing 20 people, including 17 children.

The pro-opposition Sham Network said that 40 people were killed on Thursday in Aleppo, assigning the blame on aerial bombardment as well.

The alleged attacks came just days after rebels near Damascus fired mortar shells at a school in a central Damascus district and killed 14 students and a twin car bombing against a government- controlled area in the central province of Homs that killed 100 people.