In separate incidents in a span of 24 hours, the Islamic State of Iraq and Syria (ISIS) carried out executions against two woman in Syria, sentencing them to death by stoning over allegations of "adultery".

Unconfirmed reports claim that in at least one case, the woman was sentenced to death as her new husband found that she was not a virgin.

Both incidents of death by stoning have been reported from Al Raqqa Province.

"The Islamic State carried out, for the second time in 24 hours, the punishment of Al Rajem (stoning to death for adultery) against another woman in the city of Al Raqqa in a square near the Municipal Stadium," an official from NGO Syrian Observatory for Human Rights (SOHR) stated.

The stoning, which was first reported by the SOHR, has also been confirmed by Al Jazeera which claimed that the first stoning took place in a public square in the town of Tabaqa on Thursday evening.

The report noted that the woman was tried at the Islamic Sharia court, where neither the witnesses who made the allegation were identified, nor the man - who is said to be the paramour - was charged.

"Mystery surrounds the whole thing," Abu Khalil, an activist in Raqqa who runs the anti-Islamic State group 'Raqqa is Being Slaughtered Silently', told Al Jazeera America. The group has released a picture of Thursday's stoning.

The second incident reportedly took place in a town in Raqqa, where a 26-year-old woman - identified with intials S.H.M.A. - was stoned to death by the ISIS militiants.

The SOHR report claimed that the woman was pubically executed by stoning late in the night after the Eshaa Salat, which is the last of the five prayers recited by a practising Muslim. The stoning took place in a popular market and the victim was a widow.

Raqqa, since last year, has been established as the de facto capital of the Islamic State caliphate. Since then, the region has been witnessing brutal punishments carried out by the ISIS militants under the Sharia law.

The incidents have been widely criticized on Twitter

Meanwhile in #Raqqa & for the 2nd night in a row, #IS stoned a woman to death, accused of adultry. #monstrous pic.twitter.com/Pb3T7JctvP — Hala Jaber (@HalaJaber) July 19, 2014

Extremely mournful: #Jihadists in the Syrian province of Raqqa have accused a woman of adultery & stoned her to death pic.twitter.com/wbB2nTbIyr — Hina Butt (@hinaparvezbutt) July 19, 2014

@tarekfatah @jenanmoussa @el_herself An adultery involves 2 persons, t least. Why only the woman stoned? Weird law! — Johannes Jun (@JohannesJunian1) July 20, 2014

@HDLindiaOrg If woman must be stoned to death for adultry, what about men? These mullahs who preach such things must be stoned to death — Murali Krishna (@pandu008m) July 20, 2014