The head of the Swiss Guard at the Vatican has said it is 'only a matter of time' before Rome is hit by a Barcelona-style terrorist attack.

Security has been stepped up at religious sites throughout Italy, including at the Vatican, since an Islamist murdered 86 people with a lorry in the French city of Nice last year.

Barriers and police and army vehicles have been placed around St. Peter's Basilica to make it harder for a vehicle to gather speed in an attack such as the one last week in Barcelona, when 13 people were murdered.

Despite threats from Islamic State, Rome and other Italian cities have so far been spared the kind of vehicle attacks that have also hit Nice, London and Berlin.

Swiss Guard chief Christoph Graf said his force (pictured in St Peter's Square) is prepared for a terrorist attack

ISIS terrorists have threatened Pope Francis (pictured) in videos

'It could perhaps be just a matter of time before there is such an attack in Rome, but we are prepared,' Christoph Graf, the commandant of the Swiss Guard, was quoted as telling the Swiss Catholic website Cath.ch.

Graf, referring to the attack in Barcelona, spoke on the sidelines of a religious ceremony in the Swiss city of Solothurn earlier this week.

Websites linked to Islamic State militants have made threats against Catholic targets in Rome in recent years.

Just yesterday ISIS released a propaganda video showing its fighters stamping on busts of Jesus, ripping pictures of the Pope in half and promising to come to Rome.

Barcelona: A terrorist murdered 13 people and injured over a hundred by driving a van into people walking on Las Ramblas. The Swiss Guard fear a similar attack in Rome

One of the criminals - named 'Abu Jindal' - looks straight at the camera and says in English: 'Remember this, you kuffar [an extremely offensive term for non-Muslims] - we will be in Rome, we will be in Rome'.

In 2015 in a video showing the beheading of 21 Egyptian Coptic Christians in Libya, one of the killers said: 'Safety for you crusaders is something you can only wish for ... We will conquer Rome, by the will of Allah.'

At about the same time a website used by militants ran a photo montage showing the movement's black flag flying from the obelisk at the centre of St Peter's Square.

In an ISIS video, a criminal points his gun at a printed image of Pope Francis during a ransacking of a church

Decorations - including Jesus on the cross - were also dragged down by ISIS fighters before 'kuffar' around the world were insulted in the ISIS video

The Swiss Guard has its origins as a papal protection force in the 16th century and numbers about 110 men, all of Swiss nationality.

It shares responsibility for the protection of the pope and the Vatican with a police force of about the same size.

Italian police are responsible for patrolling the Vatican's external perimeter in Rome.

Both Vatican security forces are trained in anti-terrorism tactics and in the use of modern weapons.