Libya has warned Italy about an ISIS cell in the Milan area led by a Tunisian man deported by Italy four years ago, AFP reported on Sunday.

The Italy-based militants are believed to be associates of Abu Nassim, 47, who lived in Italy in his 20s and later fought in Afghanistan and Syria then became an ISIS commander in Libya, the report said.

The network has been reportedly exposed by Libyan agents when they seized documents after government forces overtook an ISIS headquarters in the Libyan city of Sirte last week.

Italian security services are on a high state of alert for the possibility ISIS fighters from Sirte crossing the Mediterranean on migrant boats to perpetrate terrorist attacks in Italy.

Italy's Interior Minister Angelino Alfano has expelled suspected jihadist sympathizers.

On Saturday Alfano ordered a Tunsian imam in Puglia deported, though the cleric, Hosni Hachemi Ben Hassem had been acquitted of charges of recruiting jihadists.

Late on Saturday, Alfano said he had ordered the deportation of Hosni Hachemi Ben Hassem, a Tunisian imam based in a mosque at Andria in Puglia.

Alfano has signed a total of 109 expulsion orders since the start of last year, 43 of them in 2016, according to a statement.

Abu Nassim, whose real name is Moez Ben Abdelkader Fezzani, arrived in Italy in 1989. He disappeared in 1997 resurfacing in Pakistan and later joining the late Osama bin Laden's forces in Afghanistan.

He was arrested by US forces in 2001. He was transferred to Italy in 2009, acquitted of charges of terrorist recruitment in 2012 and deported to Tunisia.

Tunisia has sought to arrest him in connection with the March 2015 Bardo Museum attack in Tunis, in which gunmen killed 21 tourists and a policeman.