CATANIA, Sicily -- Prosecutors said Tuesday that they arrested the captain and a crew member of the boat in which as many as 900 people are feared to have drowned in the unremitting waves of migrants seeking to escape from war-torn Libya.
Even as the search continued for victims of the weekend disaster, coast guard ships rushed to respond to new distress calls on the high seas - two off Libya and a third boat that ran aground near Greece.
Assistant Prosecutor Rocco Liguori said the Tunisian captain and Syrian crew member were arrested aboard the rescue boat that brought 27 survivors from the deadly shipwreck to Sicily. The two were charged with favoring illegal immigration and the captain was also charged with reckless multiple homicide in relation to the sinking.
Decrying what he called an "escalation in these death voyages," Italian Premier Matteo Renzi urged Europe to put the focus on preventing more boats from leaving Libya, the source of 90 percent of migrant traffic to Italy.
"We are facing an organized criminal activity that is making lots of money, but above all ruining many lives," Renzi said at a joint news conference with Malta's prime minister, Joseph Muscat. He compared their activity to that of slave traders of centuries past, "unscrupulous men who traded human lives."
The Italian coastguard is still scouring the Mediterranean Sea for survivors of yesterday's disaster off the Libyan coast- but many here fear they'll only find more bodies, CBS News correspondent Holly Williams reported.
The European Union foreign affairs chief, Federica Mogherini, said this weekend's appalling human toll - which, if verified, would be the deadliest migrant tragedy ever - had "finally" fully awakened the European Union to the evils of human trafficking.
The EU has been under increasing criticism for lagging in its response to the crisis, with two shipwrecks believed to have taken the lives of as many as 1,300 migrants in the past week. Some 400 people are believed to have drowned in another capsizing on April 13.
Stopping the traffickers will be a key item on the agenda when EU leaders meet in an emergency summit Thursday in Brussels, along with a proposal to double spending on sea patrols off Europe's southern border. The 10-point plan includes a proposal to take "civil-military" action modeled on Europe's anti-piracy operation off the coast of Somalia, to capture and destroy boats used by traffickers.
Meanwhile, new details emerged about the weekend disaster, with Italian prosecutors saying hundreds of migrants were locked below deck unable to escape when the rickety boat capsized off the coast of Libya.
Speaking at a news conference in Catania, Sicily, prosecutor Giovanni Salvi said "a few hundred were forced into the hold and they were locked in and prevented from coming out." He said hundreds more were locked on a second level of the boat, which also had hundreds of migrants squeezed into its upper deck.
Salvi said the migrants rushed to one side of the boat as they saw a Portuguese-flagged container vessel approach, with the promise of rescue contributing to the disaster.
"Merchant ships don't have adequate training for rescues in the seas," Salvi warned. "The fact is, sea rescues are difficult and require professionalism. "
As with most such high seas sinkings, a precise death toll will likely never be known. Only 24 bodies have been recovered so far and only 27 survivors were rescued. One survivor, identified as a 32-year-old Bangladeshi, has put the number of people on board at as many as 950, though Salvi said the survivor had no means to verify numbers. He said the coast guard estimated more than 700 people were on board, based on its observations at the scene.
Muscat, the Maltese prime minister, called the latest tragedy "a game-changer," and said that "if Europe doesn't work together, history will judge it very badly."
Renzi said that recent events had proven that providing rescue wasn't always possible, given the conditions of the smugglers' boats and the delicacy of such operations, and that the focus needs to be on preventing the boats from leaving Libya. "Continuing to think that allowing them to depart and then chasing after them means putting at risk human lives," he said.
Even as European leaders grappled with how to respond to the crisis, more unseaworthy boats were setting off Monday on the perilous journey. Renzi said Italian ships were rushing to respond to distress calls from an inflatable life raft near the Libyan coast with 100 to 150 migrants on board and to another boat carrying about 300 people.
The International Organization for Migration earlier said its Rome office had received a distress call from three boats in need of help. The group says the caller reported 300 people on his sinking boat, with about 20 fatalities. No details were available about the other boats or their location, and it was not clear if they were the same rescues to which Renzi referred.
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 a trafficking ring they had cracked had generated 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.
Prosecutor Maurizio Scalia said based on telephone intercepts, the average cost to smuggle a migrant from Eritrea or Ethiopia to Libya ran $4,000 to $5,000 (euros), while the crossing to Italy cost an additional $1,000 to $1,500 (euros). Migrants pay hundreds of dollars more to get out of holding centers and at least another $1,000 to travel to northern Europe.
Payments for each leg are made up front, often using the Islamic hawala banking system which is based on an informal honor code in which a relative in northern Europe pays a local broker and the payment information is transmitted to the actual traffickers on the ground advising them that the leg has been paid for.
Authorities identified the trafficking ring's mastermind as Ermias Ghermay, an Ethiopian who has been sought since the October 2013 shipwreck off Lampedusa that left 366 people dead. He is believed to be in Libya. Authorities issued arrest warrants for 24 people, including 14 in Italy.
Renzi said the instability in Libya was giving free reign to the traffickers, as evidenced by the escalating migrant flows, but he ruled out sending ground troops to Libya or a naval blockade of migrants, saying that would only provide a corridor for them.
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.
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.
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.