A Free Syrian Army fighter helps a family after a missile fired by a jet hit the al-Myassar neighborhood of Aleppo on Wednesday. [Photo/Agencies]

A Syrian missile strike leveled a block of buildings in an impoverished district of Aleppo on Tuesday, killing at least 33 people, almost half of them children, anti-government activists said.

Many were trapped under the rubble of destroyed houses and piles of concrete, and the death toll could rise if more bodies are uncovered.

The apparent ground-to-ground missile attack struck a quiet area that has been held by anti-government fighters for many months, a reminder of how difficult it is for the opposition to defend territory in the face of the government's far-superior weaponry.

In the capital, Damascus, state-run news agency SANA said two mortar shells exploded near one of President Bashar al-Assad's palaces. It dealt a symbolic blow to the embattled leader, who has tried to maintain an image as the head of a functioning state even as rebels edge closer to the heart of his seat of power.

No casualties were reported, and it was unclear whether Assad was in the palace. He has two others in the city.

The attack was the first confirmed strike close to a presidential palace and another sign that the civil war is seeping into areas of the capital once considered safe.

Meanwhile, Syrian troops have repelled the intensified attacks of the armed rebels targeting the international airport of Aleppo, which is safe and now protected by the army, the pro-government Al-Watan Daily said on Wednesday.

The troops have thwarted an infiltration attempt by the armed groups that tried to set alight the fuel storage of the airport, the newspaper said, adding that the assailants retreated under the army's heavy firepower.