A top figure in Islamic State's self-declared police force which carries out beheadings has himself been found decapitated in eastern Syria with a cigarette stuffed in his mouth.
His mutilated body showed signs of torture, and pinned to his head was a note stating: 'This is evil, you Sheikh'.
Residents in areas controlled by Islamic State (ISIS) have said the group has banned smoking in public.
The man was an Egyptian national and was known as the deputy 'emir' of the al-Hesbah force in a Syrian province, the Syrian Observatory for Human Rights said.
Rami Abdulrahman, who runs the British-based Observatory, said it was still unclear who was reponsible for the man's death.
He said: 'We do not know whether Islamic State killed him or whether it was local people or other fighters.
'Either way it is important, because he was a very important man,' he said, adding that he believed it was the first time that an al-Hesbah member had been killed in such a way.
His corpse was found near a power plant in al-Mayadeen city in the Deir-al-Zor province.
Islamic State (ISIS), an offshoot of Al-Qaeda which has drawn in foreign fighters, has seized land in Syria and neighbouring Iraq. It has been the target of U.S.-led air strikes in both countries since September.
While ISIS has fought with other insurgents and cracked down on local populations, it has also killed its own members for what it describes as violations.
News of the emir's beheading comes just a day after pictures emerged of what appears to show ISIS soldiers executing a group of Iraqi policemen.
Entitled 'the Day of Judgement', the photos show eight Iraqi men dressed in orange Guantanamo Bay style jumpsuits.
Standing behind them, armed with pistols, are Islamic State's notorious security forces, known for carrying out mass public executions in broad daylight.
Residents and activists say ISIS has beheaded and stoned to death many people in areas it controls for being enemy fighters or for actions they see as violating their reading of Islamic law, such as adultery and blasphemy.
In December, a similar self-declared police force in western Syria decapitated four men after accusing them of blasphemy, according to the Observatory. It reported a similar killing days earlier in the north of the country.
It was also reported on Tuesday that unknown assailants also tried to kill two Islamic State militants in al-Mayadeen city.
The first attempt was when a car tried to run over a fighter near a roundabout. Another was hit by an attacker carrying a metal weapon and travelling by motorcycle, and was seriously wounded.
