BETHLEHEM (Ma'an) -- Twenty Palestinians were killed overnight Tuesday in a refugee camp in southern Syria, a Damascus-based Palestinian group said.

The coordinating committee of Yarmouk refugee camp told Ma'an that 20 Palestinians in Deraa camp were killed and dozens injured in heavy bombing by the Syrian army.

Sources in Deraa camp said that artillery shells and mortars targeted several streets near the area's mosque. It is nearly impossible to reach the injured, they added, saying that the stench of decaying bodies fills the streets.

Last week, the Yarmouk coordinating committee told Ma'an that four Palestinians were killed at a security checkpoint near the city of Aleppo.

Their bodies were found on the street and showed indications of an execution style killing, according to the group. Two other Palestinians were shot dead in their Damascus homes, it said.

On Sept. 20, at least 18 Palestinians were killed and their bodies displayed publicly in Damascus, PLO officials in Yarmouk said.

Some 225,000 Palestinian refugees have been directly affected by the 18-month-old uprising against Assad.

In August, Palestinian official Muhammad Shtayyeh said around 400 Palestinians had been killed in the internal conflict, although that figure is estimated to have significantly increased in recent months.

Activists say more than 30,000 people have been killed, including 7,000 soldiers and members of the security forces, since protests first broke out in March last year.