The warning was echoed by Pier Ferdinando Casini, the president of Italy's foreign affairs committee.
"There's always a risk of people trying to infiltrate in this way," he said.
"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."
Libyan forces launched their offensive to reconquer 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 three quarters of the city has now been liberated, a year after it was seized by Isis. There was alarm in Italy in recent days when it was revealed that Isis fighters had left behind graffiti in which they described the city as "the port of the Islamic State - the starting point for Rome".
Isis has often boasted of conquering Rome and the Vatican as key symbols of Christianity, featuring images of St Peter's Basilica in its propaganda videos.
Last week, Italy tightened security controls at commercial ports, creating long delays for passengers and vehicles boarding ferries in cities like Genoa, Palermo and Bari.
There have also been several recent terrorist attacks in Europe carried out by refugees.
Last month, Isis claimed responsibility for two cases 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.
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," said William Spindler, from the UN refugee agency.