Their convictions bring to 42 the number of people found guilty of involvement in the same smuggling ring, which was operating throughout Italy.
Italy, which has saved some 200,000 migrants at sea since the beginning of 2014, has sought to crack down on human traffickers to help deal with the huge influx of migrants reaching its shores.
U.N. Secretary-General Ban Ki-moon on Monday joined Italian Prime Minister Matteo Renzi and EU foreign policy chief Federica Mogherini on a brief visit to an Italian navy ship involved in border control operations in the Mediterranean Sea.
"Unfortunately, recently, due to political instability, in some parts of Africa, particularly North Africa, this sea has sadly become a sea of tears, a sea of misery," Ban said in a statement. "I think it seems to be the worst humanitarian crisis since the Second World War."
He said he recognizes the situation is a huge challenge for European governments.
"Not a single country - like Italy - can bear all this responsibility. In that regard, I welcome and commend the leadership of the European Union. They were united and showed their solidarity to address this humanitarian crisis and to give a better future for many people," Ban said.
He added that U.N. agencies are ready to work with the EU to prevent human trafficking and to find a political solution to the instability in northern Africa.
Renzi told Italian news agency ANSA that the visit underscores that "the entire international community is aware that this is a global problem and not a question that regards one country."