The Islamic State (IS) has renewed its threat to "conquer" Rome, publishing an image showing its flag flying from the obelisk in St Peter's Square.

Featuring on the front cover of the latest edition of online propaganda magazine Dabiq, the image is a clear signal to the Church of IS' intentions.

An article inside incites violence, urging Muslims to kill "every crusader possible...wherever they can be found."

"At this point of the crusade against the Islamic State, it is very important that attacks take place in every country that has entered into the alliance against the Islamic State, especially the US, [the] UK, France, Australia and Germany," it reads.

"Every Muslim should get out of his house, find a crusader and kill him... And the Islamic State will remain until its banner flies over Rome."

An earlier statement attributed to IS spokesman Abu Mohammed al-Adnani is also reproduced, in which he declares: "We will conquer your Rome, break your crosses, and enslave your women."

The magazine boasts of jihadis buying and selling Yazidi families captured in the Sinjar region of northern Iraq, and even claims the practice is a fundamental part of Islam.

"Enslaving the families of the kuffār [non-believers] and taking their women as concubines is a firmly established aspect of the Sharia that if one were to deny or mock, he would be denying or mocking the verses of the Qur'an... and thereby apostatizing from Islam," it says.

In a video released by IS last month, Adnani issued a further warning to the West: "You will not feel secure even in your bedrooms. You will pay the price when this crusade of yours collapses, and thereafter we will strike you in your homeland, and you will never be able to harm anyone afterwards," he said.

"O America, O allies of America, and O crusaders, know that the matter is more dangerous than you have imagined and greater than you have envisioned.

"We have warned you that today we are in a new era, an era where the [Islamic] State, its soldiers, and its sons are leaders, not slaves."

Husein Bilal Bosnić, a prominent jihadi recruiter, has insisted that the terrorist group will not stop until it is recognised by every country.

"In time the whole world will be an Islamic state. Our goal is to make sure that even the Vatican will be Muslim," he said.

According to news reports, security has been increased at the Vatican in response to recent threats.