Syrian rebels have said they planted bombs inside the army’s general staff headquarters in Damascus as President Bashar al-Assad’s forces bulldozed buildings in parts of the capital that have backed the uprising.

Syrian state television said four people were wounded in what it called a terrorist attack on the general staff compound in the highly guarded Abu Rummaneh district, where another bomb attack killed four of Assad’s top lieutenants two months ago.

“The operation targeted officers in the Assad army who have been planning and giving the go-ahead for the massacres against the Syrian people,” said a video statement by the Grandsons of the Prophet brigade, a division of the Free Syrian Army. “Bombs were planted inside the army headquarters,” said the video statement, which was broadcast on Arab satellite channels.

But as the rebels demonstrated that they could strike at the heart of the security apparatus, residents said army bulldozers had moved on the Zayat and Farouk neighbourhoods to the west, and destroyed at least 20 buildings in the Sunni Muslim areas that have sheltered the insurgents.

In the eastern Damascus neighbourhood of Hazza, footage taken by activists on Sunday showed several buildings on fire. Opposition sources said the army had stormed the area and executed 27 men.

“Any youth of fighting age seems to have been captured and killed,” said the activist Obadah al-Haj, who had fled the area.

Activist video footage from the area showed a young man lying dead beside a yellow taxi, shot in the face. Another dead youth was in the driver seat, blood covering his head and chest. Assad belongs to the minority Alawite sect, an offshoot of Shia Islam that has dominated power since members of the sect led a military coup in 1963. Assad’s father took power in 1970.

As the uprising in Syria has spread, it has become more sectarian, with activists saying Assad’s best trained forces from the mostly Alawite fourth division and the Republican guards are spearheading the fight in the capital. Assad, who is backed by Russia, Shia Iran and its Hezbollah Lebanese proxy, has lost control of rural northern, eastern and southern areas and has used helicopter gunships and fighter jets to subdue the opposition.

But the aerial bombardment has driven fresh waves of refugees into neighbouring countries, reviving Turkish calls for “safe zones” to be set up on Syrian territory.

With Russia and China blocking action by the UN security council and little appetite among western states, or Turkey itself, for committing troops to secure such zones, there is scant chance they will be set up any time soon.

Rebels said they had seized an air defence facility and attacked a military airport in the eastern province of Deir-al-Zor on Saturday. Video footage showed a walled army command centre in the province coming under attack on Sunday.

In the southern city of Deraa, which stands between Damascus and Jordan, troops continued razing and bulldozing houses in the old part of the city for a third day after army shelling and aerial bombardment drove 40,000 people from there to Jordan.

Free Syrian Army fighters had left, their light weapons no match for the firepower of Assad’s forces, residents said.

“There are around 20 homes that have been demolished and 200 burned,” said Ahmad Abu Nabout, a resident of Deraa. “Old Deraa is deserted. Troops cover up their looting by burning the homes or in some cases blowing them up.”

“Looking at the burnt and looted homes you would think these are rubbish dumps,” said Abu Anas, another resident.