Some 235,000 refugees are waiting in war-torn Libya to make the crossing across the Mediterranean Sea, according to UN figures.
"There are 235,000 people on our lists who are just waiting for the opportunity to come to Italy," said Martin Kobler, the UN's special representative to Libya, to La Stampa newspaper on Thursday.
"Strengthening security is the most important issue at the moment" in Libya, he said.
"We must tackle the problem at its roots and re-establish rule of law," the German diplomat said. "People trafficking is a crime and must be stopped."
The fight against the extremist group Islamic State was making progress in Libya, Kobler added in the interview. But he urged vigilance, because "the militants will try to move to other areas."
In March, the UN-backed unity government arrived in the Libyan capital Tripoli, amid international hopes it would be able to re-establish stability in the oil-rich country.
However, a rival parliament, based in the eastern city of Tobruk, has refused to recognize the Tripoli government.
Libya fell into anarchy following the overthrow of longtime dictator Moamer Gaddafi in a 2011 uprising.