In a separate incident, at least three people, including a child, were killed and 93 others were rescued when a wooden boat carrying dozens of migrants who had departed from Turkey ran aground off the Greek island of Rhodes.
Dramatic video showed migrants clinging to pieces of wreckage and rescuers helping them ashore.
Prosecutors in Palermo, meanwhile, said the human trafficking ring they cracked had been involved in transactions worth hundreds of thousands of euros crisscrossing Europe as migrants paid not only to cross the Mediterranean but also to join relatives in northern Europe.
They identified the mastermind as an Ethiopian, Ermias Ghermay, who has been sought since an October 2013 shipwreck off Lampedusa, Italy, that left 366 people dead. He is believed to be in Libya. Authorities issued arrest warrants for 24 people, including 14 in Italy.
Meanwhile, the search continued for victims of the weekend shipwreck. Only 24 bodies, all men, have been recovered so far, and they were brought Monday aboard the coast guard ship Gregoretti for burial in Malta. The 27 survivors were to be brought later to Sicily by the same ship.
Capt. Gian Luigi Bove told reporters in Malta his vessel was about 80 kilometers (50 miles) away from the shipwreck when the distress call came in, and that they discovered two survivors when they arrived around 2 a.m. Sunday, along with bodies, floating in the sea.
The survivors were taken on board. He said there was no sign of the smuggler's boat, an indication that it may have already sunk.
Bove said the survivors were from sub-Saharan Africa and language issues were impeding the investigation.
Libya is a transit point for migrants fleeing conflict, repression and poverty in countries such as Eritrea, Niger, Syria, Iraq and Somalia, with increased instability there and improving weather prompting more people to attempt the dangerous crossing.
That instability will be a focus when EU leaders meet Thursday for their summit in Brussels. Renzi ruled out sending ground troops to Libya or a naval blockade of migrants, saying that would only provide a corridor for the smugglers.
Fighting in Libya has escalated to its worst levels since the 2011 civil war that ended with the overthrow and killing of longtime dictator Moammar Gadhafi.
Rebel groups that fought against him kept their weapons and militias have mushroomed in number. The country now has rival governments - the internationally recognized one in the eastern city of Tobruk, and an Islamist-backed one in the capital, Tripoli. The two sides have been negotiating in Morocco to end the fighting.
Malta and Italy are closest to the Libyan coast, and have received the brunt of a migrant tide that carried 219,000 people from Africa to Europe last year. Some 3,500 died or went missing along the way, the U.N. High Commissioner for Refugees Antonio Guterres said in a statement Sunday.
Mired in economic crisis and a facing a surging anti-foreigner electorate in many nations, there is little appetite across European governments to take in more poor migrants, however desperate their plight.
Czech Foreign Minister Lubomir Zaoralek said sending more ships to rescue migrants could actually make the problem worse.
"If we make the work of traffickers easier and accept refugees that have gone overboard, this will make it an even better business for them," he said on Czech television. "We need to find a way to prevent people from setting out on such ships."