Three Syrian men have allegedly been beheaded by terror group Isis (Islamic State) for cursing.

The execution was carried out in the Syrian city of Raqqa, the capital of the Islamic Caliphate declared by IS last August.

The men were charged with "cursing the Lord in markets, streets, and homes," El Gulf Daily reported.

According to IS' version of sharia law, imposed in the areas of Syria and Iraq controlled by the group, cursing is punished with beheading.

The picture of the alleged decapitation was posted on Twitter by user Military Studies.

Beheading as Routine Practice in Raqqa

IBTimes UK was not able to independently verify whether the beheading took place. However, other reports of Syrian civilians being beheaded by the terror group have emerged this year.

Website Raqqa is Being Slaughtered Silently - created by activists who aim to show the brutalities carried out by the insurgents in the Syrian city - routinely posts videos and pictures of civilians beheaded or massacred by the militants.

One if its latest posts reads: "Raqqa has remained an IS stronghold since the group took control of the city last year. Residents have been subjected to an unrelenting torrent of horror, with many too poor to flee across the border to Turkey."

According to Sky News, IS has condemned the activists as "enemies of the Lord" and reportedly executed one, Motaz Billah, after tracing him through Facebook.

In an interview with Radio Free Europe, a Syrian activist described Raqqa as a "ghost city", now that hundreds of people have fled since IS took control last August.

"The executions are a little bit less now, because there are fewer people to be executed. But last Friday [17 October] they executed two people here in the public square.

"One of the men who was executed had committed the crime of 'saying a bad word about Allah'.

"There had been an altercation between some IS militants and the man's parents. The man joined in and was arrested. The man became angry and said the 'bad word.' So they executed him."

According to recent reports, people in Raqqa have also been banned from owning academic books, studying subjects including law and human rights, and educating children privately at home.

Teachers have been told they must have training in IS' interpretation of sharia, and should avoid certain subjects in curricula and exams "which do not conform to sharia law",