BEIRUT (Reuters) - A man and a woman have been stoned to death for adultery in separate executions in jihadist-controlled areas of Syria, a monitoring group reported on Tuesday.

The man was executed in Idlib province in an area controlled by Islamist groups including the Nusra Front, al Qaeda’s official affiliate in Syria, said the Syrian Observatory for Human Rights, which tracks violence on all sides of Syria’s civil war.

It is the first documented case of a man being stoned to death for adultery since Syria descended into civil war in 2011 and hardline Islamic groups emerged as powerful players in areas that slipped from government control, the Observatory said.

The woman was executed in Hama province in an area controlled by Islamic State, an al Qaeda offshoot that has seized swathes of Syria and Iraq and is being targeted by U.S.-led air strikes, the Observatory said.

A video posted online appeared to show her execution. A bearded fighter is shown passing down the sentence in the presence of other gunmen and her father, who appears to approve of her execution.

Her hands and feet are then tied with a rope and she is forced to kneel in a pit. Covered head to toe, she begins to pray out loud as large rocks are seen striking her body. The video shows the logo of Islamic State.

The two incidents, which Reuters could not independently verify, appear to be unrelated.

The woman’s execution was the third of its kind in Islamic State-run territories in Syria, according to the Observatory.

Islamic State controls around a third of Syria and Iraq after having acquired new territory with lightening speed earlier this year. It quickly established a fierce reputation by crucifying, beheading and carrying out public executions of anyone deemed a threat to its rule.

Islamic State routinely carries out sentences of lashing against men in territories it rules for offences that range from adultery and subversion to blasphemy and missing prayer time.

In July, Islamic State stoned two women to death under similar circumstances to the Hama stoning. One was of a 26-year-old widow, according to the Observatory.

Syrian society is unaccustomed to sentences like stoning and lashing. For decades, the country was ruled by a government that implemented a mixture of Islamic and secular laws. Offences such as adultery were rarely prosecuted.

The fighter overseeing the woman’s execution appears to lay the blame for her crime on her husband, suggesting he had been absent. He urges “all men to treat women well” before the stoning begins.

“Do not leave women. Do not be absent from them for longer than the time period permitted (by Islamic law). Return to God, brothers. And take good care of women,” he says.

At one point he addresses the woman as “honorable sister”, and asks her for final words. “I advise every woman to protect her honor more than her life,” she says. And I ask every man, before he marries off his daughter, to scrutinize her new marital environment. That’s all,” she says in a faint voice.

It is not clear exactly when the video was shot, or how the woman was found guilty of adultery - a conviction that would require at least four witnesses according to Islamic law.