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, Reuters reported, where another bomb attack killed four of President Bashar al-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.
And Mufa Hamze, vice president of the Damascus military council of the Free Syrian Army, also claimed in an interview with The Daily Beast that the bombs had been planted inside the headquarters itself, and that the attack was in retaliation for recent mass killings reported in the Damascus suburb of Daraya.
"The bombs were inside the building," he said, and added that though he had no casualty reports, he believed a number of senior officers were present at the time of the attack.
"These officers were involved in the massacre, and they felt no remorse for the loss of Syrian blood," he said. "It was revenge."
But as the rebels demonstrated they could strike at the heart of the security apparatus, residents said army bulldozers moved on al-Zayat and Farouk neighborhoods to the west, and destroyed at least 20 buildings in the Sunni Muslims districts that have sheltered the insurgents.
In the eastern Damascus neighborhood of Hazza, footage taken by activists on Sunday showed several buildings on fire. Opposition sources said the army had earlier stormed the area and summarily executed 27 young men.
"Any youth of fighting age seems to have been captured and killed," activist Obadah al-Haj, who had fled the area, told Reuters.
Opposition 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.
The U.N. children's fund UNICEF said Sunday that 1,600 Syrians had been killed in civil war last week alone, making it the deadliest seven-day period of the 18-month conflict, the Voice of America reported.
UNICEF spokesman Patrick McCormick said the death toll included some children, but he did not elaborate or say how he obtained the figure.
In Tehran, Iranian Deputy Foreign Minister Hossein Amir-Abdollahian announced late Saturday that a "troika" of representatives from Iran, Egypt, and Venezuela had been named at the Non-Aligned Movement summit to help resolve the Syrian crisis, the Tehran Times reported.
He also said Iran -- just about Assad's only remaining friend in the region -- welcomes the proposal from Egyptian President Mohamed Morsi for the establishment of a contact group on Syria that would include Egypt, Iran, Saudi Arabia, and Turkey.