Christians living in Sweden have been warned to 'convert to Islam or die' in a string of threatening messages linked to the Islamic State.

Members of the Assyrian community are understood to have been targeted with sinister graffiti daubed on restaurants and businesses in Gothenburg – a hotbed for jihadist recruitment.

The messages bear all the hallmarks of the chilling psychological warfare employed by ISIS in the Middle East, but as yet Swedish police have been unable to track down those responsible.

Markus Samuelsson, one of 3,000 Assyrian Christians living in Gothenburg, said he found the walls of his restaurant covered with the messages 'convert or die' and 'the caliphate is here'.

Chilling: Christians living in Sweden have been warned to 'convert to Islam or die' in a string of threatening messages linked to the Islamic State (seen, above, in the terror group's Syrian stronghold of Raqqa)

The latter is a reference to the terror group's attempt to create a warped form of Islamic government which has seen it clamp down on religious freedoms with shocking brutality across Iraq and Syria.

Mr Samuelsson, who owns Le Pain Francois, told Swedish daily Dagens Nyheter: 'I felt a sudden chill down my spine. It's terribly painful. We feel threatened.'

The same messages, along with the ISIS logo, were also painted on a neighbouring pizzeria, while other non-Assyrian-owned businesses were left unscathed, it was reported by Breitbart.

The warnings were also accompanied with the Arabic letter ن – a symbol which has been used ISIS in the Middle East to donate Christians.

Some 150 jihadists – more than from America – are believed to have left Gothenburg (above) to join ISIS

It was painted on doors of Christian homes in Mosul, Iraq, to allow militants to identify and drive them out when they seized the city last year.

At least 150 jihadists – more than from the United States – are believed to have left Gothenburg to join ISIS, according to Swedish newspaper Aftonbladet.

Meanwhile, terrorism expert Magnus Ranstorp has called the city 'the Swedish Centre for Jihadists'.

Earlier this week, the U.S. State Department released a report detailing how ISIS had spearheaded a campaign of attacks last year by militant extremist groups on religious freedom across the world.

In the territories of its would-be caliphate, it said ISIS militants have forced centuries-old Christian communities to convert, pay a ruinous tax or die, while kidnapping, selling and raping thousands of women and children on the basis for their faith.

Assyrians, who are indigenous to the Middle East, are one of the oldest branches of Christianity, dating back to 1AD.