Ambassador Pontesilli also refuted the reports that Italy sometimes send Nigerian migrants from Italy to Libya.
He said some of the inmates are repatriated to Nigeria upon the completion of their jail terms.
The envoy disclosed this in an interview with journalists in Abuja.
Pontesilli said, "In Italy we have about 1500 Nigerians in jail for various offences. It is a big number.
"We sometimes send them back to Nigeria once they finished their terms because they have not behaved well."
But the ambassador refuted the reports that Italy sometimes send Nigerian migrants from Italy to Libya.
"Never, we never sent anyone not even one single person to Libya. Some Nigerians are stuck in Libya because they were never able to cross over to Italy, but all those who went to Italy no one, not even one was ever sent back," he said.
"All Nigerians who have reached Italy and are behaving well have no problem. Not one of them not even one has heard of being sent back to Libya.
"Thank God the government is doing a lot to repatriate them through chattered flights. Thanks for the help from the European Union and the International Organisation for Migrations that are slowly repatriating them back to Nigeria."
Pontesilli noted that the relationship between Italy and Nigeria remains stronger, stronger than ever. adding that Italy had a lot in trying to help Nigeria maintain security and stability.
He said, "This to Italy is very important, the stability and the security of Nigeria is our foremost consideration.
"We think that without a stable secure country there cannot be development. So that’s why we stand strongly behind President Muhammadu Buhari trying to establish a strong, safe and stable Nigeria.
"This to us is the number one priority of the country, we are doing all we can to support this".
The ambassador also mentioned that the government of Italy has helped train many Nigerian officials from the military, police and immigration.