IS magazine Dabiq
The front cover of IS magazine DabiqTwitter

The Islamic State (IS) group renewed propagandist threats against Rome and the Vatican in a new issue of its official magazine, which had a Photoshopped picture of a jihadi flag flying atop the Holy See on the front cover.

The extremist group formerly known as Isis has tried to characterise a US-led effort to counter its advance in Iraq and Syria as a religious war akin to medieval Christian crusades.

According to the group's rhetoric, all westerners are offspring of the cradle of Christianity, Rome, which in turn becomes a symbolic target.

IS reaffirmed such credo in the fourth issue of its English language magazine, Dabiq, which ran a cover story titled The Failed Crusade.

"Rome in the Arabic tongue of the Prophet refers to the Christians of Europe and their colonies in Shām [Greater Syria]," the article read.

It was accompanied by a picture depicting IS's black flag risen atop the Egyptian obelisk at the centre of St. Peter's Square, in the Vatican.

The magazine reproduced parts of an earlier statement attributed to IS spokesman Mohammed al-Adnani, claiming jihadists will one day conquer Rome.

"We will conquer your Rome, break your crosses, and enslave your women, by the permission of Allah, the Exalted," Al-Adnani said. "If we do not reach that time, then our children and grandchildren will reach it, and they will sell your sons as slaves at the slave market."

In the last section of the 12-page piece, the Islamist militants' mouthpiece called on jihadi sympathisers across the world to attack westerners "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," the article read.

"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."

Rome was first singled out as a target also by IS leader Abu Bakr al-Baghdadi in its first statement since the group changed name from Isis to an Islamic "caliphate" earlier this year.

Baghdadi's Ramadan message was followed by rumours of possible attacks against the Vatican and Pope Francis that were played down by the Holy See.

IS militants have been accused of atrocities including crucifixions, torture and summary executions carried out against Western journalists and aid workers as well as religious minorities and fellow Muslims.