A little-known militant group claimed responsibility in a video posted online on Saturday for the twin bombing in Syria's capital that killed at least 55 people earlier in the week.
The video was narrated by a man whose voice was garbled to disguise his identity. There was no decisive proof in the video to show suspected Islamist group al-Nusra Front had a hand in the operations, which the government said were suicide bombings.
The video showed no images of militants making or setting up the bomb and did not claim the attack as suicide bombings.
A video clip of black smoke rising over Damascus from the day of the blast was shown at the end of the statement, labelled as coming from the "Camera of the Mujahideen (holy warriors)".
Activists and the rebel Free Syrian Army say they had nothing to do with the bombings and say the blasts were orchestrated by state forces to hurt the opposition's image.
The online video said the blasts were in response to security force strikes on rebellious towns that have shared in the 14-month-old revolt against President Bashar al-Assad.
"Al-Nusra Front, God strengthen it, undertook a military operation in Damascus against the dens of the regime to target the Palestine and Dawriyat (security) branches. This is due to the regime's continued strikes on residential neighbourhoods in the Damascus suburbs, Idlib, Hama, Deraa and other areas," said a man's voice on the video, reading from text shown on screen.
"We tell the regime: Stop your massacres of Sunni people or you will bear the sins of the Alawites. What is coming will be more disastrous. We ask Sunnis to avoid any security force branches or other dens of the regime."
Syria's uprising against four decades of Assad family rule was fuelled by its Sunni Muslim majority, many of whom are resentful of a political and military elite dominated by Assad's minority Alawite sect, which is an offshoot of Shi'ite Islam.
The turmoil in Syria has sparked sectarian tensions in some parts of the country.
The Syrian government points to the bombings as proof it is confronting foreign-backed militants, not a home-grown uprising, which it says have killed more than 2,600 security personnel.
The al-Nusra Front has previously claimed responsibility for other bombings in Damascus and Aleppo. Its latest video was not posted on commonly-used Islamist sites, where most Al Qaeda statements and the group's previous announcements have appeared.