The safety and wellbeing of Christians living in Syria is worth up to 17 grams of gold, according to a statement from one Islamist rebel faction posted to the internet on Wednesday.

When 'The Islamic State of Iraq and the Levant' (ISIL) took control of the city of city of Ar-Raqqah in northern Syria, on the northern bank of the Euphrates, they reportedly presented the Christian residents with three options.

These were: converting to Islam; submitting to a form of Islamic rule under which non-Muslims would be second class citizens; or rejecting ISIL and their rules and being executed.

According to statements from ISIL, 20 Christian leaders chose the second option.

The levy of gold that was added to the agreement is based on an Islamic practice known as 'jizya', a tax paid only by non-believers living in states ruled by Islamic Sharia law.

It requires that up to 17 grams of gold be provided by every Christian man in the region in exchange for what ISIL has called "safety", according to Almanar News.

ISIL argues that this is because Christians, and all other non-Muslims living within the area they control, fall under the second class citizen category of 'dhimma'.

This principle has its origins in seventh century Islamic teachings, but was abolished in most of the Middle East under reforms by the Ottoman Empire passed in the nineteenth century.

Ar-Raqqah was the first and only city to fall totally under rebel control in 2013. In January, ISIL fought off an offensive by rival Islamists and more moderate anti-Assad rebels.

ISIL are also instituting bans on the sale and consumption of alcohol or pork, repairs or renovations to church buildings, ringing of church bells, external displays of non-Islamic religious symbols, public non-Islamic prayer, and ownership of weapons by non-Muslims.

Some of these regulations had been noted previously, but this week ISIL announced newer, stricter rules, that specifically applied to Christians.

ISIL have also changed the official weekend of the city. Instead of Friday and Saturday, it will now be held on Thursday and Friday.

Examples of this kind of imposition of strict interpretations of Islamic law raise serious concerns from Western and Arab supporters of the Syrian opposition.

They are concerned that those wanting to overthrow President Assad may attempt to turn Syria into a theocratic state based on Sharia law.

This would lead to institutionalised violations of human rights for Christians, Jews, Atheists, Homosexuals, Muslims from other denominations, and many other groups.

ISIL is an Al-Qaeda splinter group that is composed mostly of Takfiri militants. In Arabic, Takfiri refers to a Muslim who accuses another Muslim of defecting from Islam. The word has its origins from the word kafir which means 'infidel'.

As a denomination of Islam, Takfiris believe in an extremely strict interpretation of the Koran, accepting no interpretations or understandings not present at the time of Mohammad.

Al-Qaeda has denounced ISIL for failing to accept the possibility of arbitration in Syria, and for taking part in fighting against other anti-Assad factions, resulting in the deaths of several thousand people.

Abu Mohammed al-Julani, a representative of the Syrian Al-Qaeda affiliate group, the Al-Nusra Front, has been quoted by the BBC saying: "If you refuse God's ruling, and do not cease afflicting the ummah [Islamic community], it [the community] will act against this aggressive, ignorant way of thinking and banish it."

The ultimatum gives ISIL five days to comply, otherwise the Al-Nursa front will "eradicate" ISIL, according to Al Jazeera.