Islamic State, which split from al Qaeda and has seized land in Iraq and Syria, has beheaded and stoned to death Syrian and foreign civilians and combatants for crimes it sees as violating its strict interpretation of Islamic law.
But Nusra Front, which sometimes fights alongside Western-backed insurgents in Syria as well as against them, has also carried out such killings or physical punishments after accusing people of violations such as insulting God or thievery.
Both groups have been targeted by U.S.-led strikes which started last year.
Rami Abdulrahman, director of the Britain-based Syrian Observatory for Human Rights, said he received a video showing the woman being shot in the head outside Idlib city after being charged with adultery. Before she was killed, she begged to see her children but her killer refused, he added.
Photos posted on Twitter said to be of the woman showed her dressed in a black robe, headscarf and a red jacket and crouching on a pavement next to a group of standing men who appeared to be from Nusra Front. One man clothed in black wore a balaclava and held an assault rifle.
Other photos showed her falling to the ground beside a wall sprayed with Nusra Front’s name and then her body on the ground.
Nusra Front controls between 70-80 percent of Idlib, Abdulrahman said. Hardline groups such as Islamic State and Nusra Front have become the most powerful insurgent forces in Syria’s nearly four-year conflict, undermining rebel fighters the United States and its allies say they want to train and equip. -Reuters