Three survivors who were rescued said there were 120 people on the boat, Flavio Di Giacomo said.
“There are therefore 117 missing people including 10 women and 2 children (one was just 2 months old),” the spokesman wrote on Twitter.
He added that many of the migrants on board were from West Africa, but there were also about 40 Sudanese on board, according to those who survived.
The survivors were rescued by the Italian coastguard on Friday and brought to the island of Lampedusa.
The coastguard had originally said just 20 people were on board the boat, which found itself in distress 50 nautical miles (92.6 km) north-east of Tripoli.
Di Giacomo later told Italian media that the incident could be a much worse tragedy.
“They told us that 120 people were on the dinghy that set out from Libya on Thursday night,” Di Giacomo told the Adnkronos news agency. “After 10 to 11 hours at sea, the boat began deflating and started to sink. The people fell into the sea and drowned.”
However, there were further contradictory figures from a Libyan Navy official, who said he believes about 50 migrants are still missing.
A Libyan coastguard boat broke down while it was on its way to rescue the sinking boat on Friday, Ayoub Qasim, spokesman for the Libyan Navy, told dpa.
In a separate incident on Saturday, the Libyan coastguard intercepted a total of 87 people aboard two boats off the capital Tripoli, Ayoub said.
They included 11 women and eight children, according to the official.
Libya descended into chaos following the 2011 revolt that toppled long-time dictator Moamer Gaddafi.
The North African country has since emerged as a gateway to Europe for people fleeing war, persecution and poverty in their homelands.
Italy has largely closed its ports to migrants in a bid to deter them from attempting to reach its shores. However, people are still dying on the dangerous crossing.
Since the beginning of the year, 83 people have been killed in the Mediterranean, according to the IOM. In the same period last year, there were 199 deaths.
“As long as Europe’s ports remain open, as long as someone helps the smugglers, unfortunately the smugglers continue to do business and continue killing,” Italy’s right-wing Interior Minister Matteo Salvini said.
Since Italy’s new populist government decided in June to close its ports to migrant rescue charities, EU governments have clashed on how to handle incoming asylum seekers from North Africa.
Rome’s hardline stance recently left two German charity rescue boats with dozens of migrants stranded for weeks in the Mediterranean until eight EU nations agreed to take them in.
On Saturday, one of the two German NGOs at the centre of that row said it had picked up 47 people at sea.
Sea-Watch said on Twitter that one of its vessels had found them and that “all are safe and being cared for.”
It is unclear where these migrants will be taken, with a spokesman for the NGO, Ruben Neugebauer, saying all “relevant points” have been contacted. – DPA/Bernama
