BETHLEHEM (Ma'an) -- Gunmen from the Free Syrian Army on Friday assassinated a Palestinian leader in Deraa refugee camp, the Palestinian Front for the Liberation of Palestine - General Command said.

Free Syrian Army rebels shot dead PFLP-GC leader Adel Hasan in the southern Syrian city, PFLP-GC said in a statement.

PFLP-GC added that Palestinians would continue to support the Syrian people and resist "terrorists" trying to overthrow President Bashar Assad.

Hossam Arafat, a member of the PFLP-GC politburo, said Ihsan had been active in trying to stop FSA rebels from using Deraa camp as a base. Arafat said rebel forces were attacking Palestinians in refugee camps in Syria.

Earlier in October, Assad's forces bombed Deraa camp killing at least 20 Palestinians and injuring dozens more, Palestinian refugees in Damascus told Ma'an. Sources in Deraa camp said that artillery shells and mortars targeted several streets near the area's mosque.

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.

Activist group Avaaz said Thursday that at least 28,000 Syrians had gone missing since they were abducted by forces loyal to Assad during the 19-month-old revolt. Other rights groups have also accused Syrian rebel groups of abducting people they deem pro-government.

One Syrian-based human rights organization reported up to 80,000 people had disappeared, added Avaaz, a campaign network that aids opposition activists in Syria alongside other causes worldwide.

The figures could not be verified independently.

Activists say 30,000 people have been killed in Syria's conflict which started with peaceful protests but turned violent after months of oppression.