Damning new accusations against Assad regime

BEIRUT -- Activists say Syrian government forces have killed at least 20 civilians while targeting rebels in the northwest who have been advancing in recent weeks.

The airstrikes and shelling in Idlib province overnight targeted rebels in areas north and south of the town of Jisr al-Shughour, which recently fell to the insurgents, and in and around the town of Saraqeb.

The Britain-based Syrian Observatory for Human Rights said Thursday at least 21 civilians, including five children, were killed.

The insurgents have been advancing in Idlib province in recent weeks, capturing the provincial capital as well as Jisr al-Shughour and a military base.

Activist groups on Wednesday said government helicopters had dropped explosives-filled barrels containing chlorine on Saraqeb. The reports could not be independently verified.

President Bashar Assad's regime has been accused repeatedly of using both the indiscriminate barrel bombs and chlorine in civilian areas in recent years, with reports increasing since the documented destruction of the government's declared chemical weapons stockpile.

Assad agreed to the collection and destruction of those weapons, which included sarin gas and other military-grade chemical toxins, under huge international pressure and the threat of military action by President Obama.

Chlorine, however -- a common chemical used in everything from swimming pools to cleaning products -- was not listed as a chemical weapon and is still readily available inside Syria. While far less lethal than sarin and other military chemical agents, and much harder to effectively weaponize, it can be added to traditional explosives to cause dramatic breathing problems and, perhaps more significantly, panic.

President Obama seemed poised to launch attacks on Assad's military positions inside Syria following a large-scalesarin gas attack on rebel-held territory in the densely packed eastern suburbs of Damascus in August 2013.

The U.S. government and aid groups said there was indisputable evidence the gas-laden shells were fired by Assad's military, but the president himself has repeatedly denied using chemical weapons, or the deadly barrel bombs, against his own people in interviews with "CBS This Morning" co-host Charlie Rose.