At least five people were killed and more than 20 wounded on Thursday in a bomb blast near a security headquarters in Syria's central Hama city, a monitor said.

"A truck packed with explosives detonated... near a branch of the military intelligence, killing at least five people and injuring more than 20," the Syrian Observatory for Human Rights said.

Syrian state television also reported the blast, saying four people had been killed and 22 wounded in a "terrorist explosion" at the southern entrance of the city.

In the northern province of Raqa, two suicide bombers exploded inside base 17, an army base under siege by opposition forces, according to the Observatory, a Britain-based group that relies on activists and other witnesses inside Syria.

The group said two fighters from the jihadist Islamic State of Iraq and the Levant had blown themselves up at the headquarters, which is north of the group's stronghold in Raqa's provincial capital.

Clashes between regime forces and ISIL broke out after the blasts, which the Observatory said killed several soldiers.

In Damascus meanwhile, the group said a man died after regime shelling a day earlier on the Palestinian Yarmuk camp, where a ceasefire has broken down.

The renewed fighting has halted aid delivery efforts to the besieged camp, where two more people died from lack of food and medical care on Wednesday, the Observatory said.

Around 130 people are reported to have died because of shortages in the camp caused by the tight army siege.

More than 140,000 people are estimated to have been killed since the start of the uprising against President Bashar al-Assad in March 2011.