At least 55 people were killed and dozens injured Thursday morning when two powerful roadside bombs exploded on a freeway south of Damascus, Syria's official SANA News Agency (ITALICS) reported.

According to SANA, the bombs were detonated on a freeway near the Qazaz neighborhood as people were driving to work and taking children to school.

Horrifying images of smoldering vehicles, some with the charred remains of victims inside, were aired on state-run television. The government blamed "terrorists" for the devastation -- an accusation Syrian President Bashar al-Assad has repeatedly made during the 14-month uprising.

One resident said security forces cordoned off the Kfar Souseh district where the country's military intelligence complex resides. He said troops were firing their automatic rifles in the air.

Thursday's dual bombing comes one day after an attack on a U.N. convoy in the southern city of Deraa injured six Syrian soldiers, including one officer, escorting the convoy. None of the U.N. observers were injured. In a separate incident Saturday, a bomb near a security installation destroyed nine vehicles.

On Wednesday, U.N. Secretary-General Ban Ki-moon decried the recent rash of roadside bombings, warning that civil war is imminent.

"(Both sides) must realize that we have a brief window to stop the violence -- a brief opportunity to create an opening for political engagement between the government and those seeking change," Ban said.

The Syrian Observatory for Human Rights says nearly 12,000 people have been killed, mostly civilians, since the uprising began in March 2011, a few months after the "Arab Spring" protestors in Tunisia and Egypt brought down their respective governments.