Libyan authorities have warned Italy of the presence of a Milan-based cell affiliated to the Islamic State terror group.

The revelation was made after Libyan authorities seized some documents when government troops took over an IS headquarter in the city of Sirte earlier in August.

It is believed the cell is associated with Abu Nassim, a 47-year-old Tunisian man who lived in Italy before becoming an IS commander in Libya, AFP reported.

The news came as Italian authorities ordered the expulsion of a Tunisian national accused of planning an attack at the Leaning Tower of Pisa. Bilel Chiahoui, 26, was arrested after he posted on social media messages threatening to attack the monument.

On 13 August, Interior Minister Angelino Alfano also ordered the expulsion of Tunisian imam Hosni Hachemi, accusing him of inciting racial hatred. Hachemi was also accused of recruiting fighters for terrorist cells, but he was later acquitted.

IS has repeatedly threatened to attack Italy. The latest of such threat was made earlier this month, when the group released a video claiming it would conquer Rome.

The Islamist outfit also claimed that Sirte was a gateway to Rome in a graffiti found on the walls of Sirte by a militia group loyal to Fayez al-Sarraj's national unity government. The militias, which have helped liberate most of Sirte, photographed the graffiti earlier in August.

Rome features heavily within IS's teachings. The terror group's distorted view of Islam claims that IS will eventually face and defeat an army from "Rome", which will lead to the rise of an 'anti-Messiah' figure who will in turn defeat IS and trigger Armageddon – the ultimate goal of IS's founders.

However, it's unclear what "Rome" refers too: it could refer to Turkey (once the base of the Eastern Roman Empire) or any military force that opposes IS.

Libyan forces began their offensive to recapture Sirte in May. The advance was slowed due to major causalities caused by IS landmines and snipers.

IS fighters who have been routed from their former stronghold of Sirte in Libya could try to enter Europe by hiding among migrants heading across the Mediterranean in smugglers’ boats, Italy has warned.

Hundreds of Islamic State of Iraq and the Levant fighters are fleeing Sirte after coming under sustained assault by Libyan ground forces and air strikes by US fighter jets and drones.

There is now a much greater risk that some terrorists could attempt to pass themselves off as migrants or refugees, according to the head of the parliamentary committee that oversees the Italian intelligence services.

If they were successful in reaching Italy, the IS members could plan attacks on targets in Europe.

 “The scenario has totally changed and the risk that militants could flee to Europe by sea has substantially increased,” said Giacomo Stucchi, the president of the intelligence committee.

“For a long time it seemed improbable, if not impossible, that IS would put its fighters on migrant boats, putting at risk men in whom it had invested time and money,” said Mr Stucchi. 

“But now there is total chaos, and in trying to escape from Libya those who are not heading south (into the desert) could try to cross by sea to Europe. 

“They are loose cannons, men on the run. We need to understand their intentions – whether they want to disappear without trace, or whether they want to continue fighting in the name of their cause.”

Libyan forces launched their offensive to reconeuer Sirte in June. After weeks of house-to-house fighting, they recently captured several strategic locations formerly occupied by the terrorist group, including the Ouagadougou convention centre, a symbol of the extremists’ control of the city. 

Libyan officials claim that three-quarters of the city has now been liberated, a year after it was first seized by IS.

The warning that IS fighters might try to reach Europe in migrant boats and rubber dinghies leaving from the Libyan coast was echoed by Pier Ferdinando Casini, the president of the foreign affairs committee in the Italian Senate. 

“There’s always a risk of people trying to infiltrate in this way. But the priority for us was to liberate Sirte. This is a great victory for the forces of the coalition and the (UN-backed) government of (Fayez) Al-Sarraj.”

Italy last week tightened up security controls at commercial ports, with passengers and vehicles boarding ferries in cities like Genoa, Palermo and Bari facing long delays. 

There have been several recent terrorist attacks in Europe carried out by by refugees.

Last month, Isil claimed responsibility for two attacks in Germany - an axe attack by a 17-year-old Afghan refugee and a suicide bombing by a Syrian refugee which injured about 20 people.

Another Syrian refugee was arrested in July after killing a pregnant woman with a machete in Germany, though police said the murder did not appear linked to terrorism. And last week, German police arrested another Syrian refugee after receiving a tip-off that he was planning a possible Islamist-motivated attack.

The United Nations has warned against demonising refugees and migrants on the basis of isolated, if devastating, acts of violence.

"We should not forget that the vast majority of refugees are law-abiding and we should not demonise them or see them all as criminals and terrorists because that's not the case," William Spindler, of the UN refugee agency, told Reuters.