By Anthony Faiola and Brian Murhpy / Stefano Pitrelli contributed to this report

BERLIN — Spurred by Sunday’s migrant disaster, which authorities feared would be the deadliest ever in the Mediterranean Sea, the European Union on Monday vowed to ramp up lifesaving search-and-rescue operations even as more rickety vessels bound for Europe fell into distress.

In a candid mea culpa, European officials conceded that they had acted too slowly to address what has become a mounting humanitarian emergency on the continent’s southern flank. They announced a 10-point proposal to shore up its refugee management system, including an effort to seize and destroy the ships used by migrant traffickers.

Any new steps require further endorsement by European leaders, who are set to consider the plan Thursday at an emergency summit on the migrant crisis.

Officials could not immediately estimate how long it might take to put the new measures into effect. But the proposals included what could be as much as a doubling of resources and a broader remit for the E.U.’s regional border operations in the Mediterranean and elsewhere.

“We need to act, to act fast and act united,” Federica Mogherini, the E.U.’s high representative for foreign affairs, said after a meeting of E.U. ministers in Luxembourg. She said Sunday’s tragedy off the coast of Libya — in which hundreds of migrants, including many locked in a hold, are believed to have lost their lives — had focused Europe on the refugee crisis in the same way the January shooting attacks in Paris had drilled home the problem of home-grown terrorism.

Acknowledging that the region had waited too long to respond, Mogherini added: “We don’t have to be afraid of showing the limits of institutions and the decision-making process. This is sad, this is not a justification, and I’m afraid we will not find justification.”

[The annual tragedy of ‘migration season’ ]

Reactions to the E.U. effort, however, were mixed, with some observers saying there was not enough detail about how and when the plan would change a situation that has already reached desperate levels. Some lauded the E.U. for proposing broader action, particularly on search-and-rescue operations. But others said the plan was vague.

And not all of the proposals would give migrants reason to celebrate. One measure involved a plan to “rapidly” assess and return to their home countries those who did not qualify for political or humanitarian asylum. Other efforts were aimed at the traffickers who are ferrying migrants to Europe.

Karl Kopp, a spokesman for the Berlin-based rights group Pro Asyl, called for emergency reception centers in Italy and Greece and other immediate action to aid migrants.

“Considering how dramatic the situation is, this is a joke,” Kopp said. “This 10-point plan does not do justice to the mass dying in any way.”

The dangerous journeys from North Africa and elsewhere have gone on for years, but now a surge is unfolding. Officials estimate that as many as 1 million migrants are bottlenecked in lawless Libya, having arrived there from pockets of misery and conflict in Africa, the Middle East and beyond.

The number of migrants crossing the Mediterranean rose sharply last year to more than 220,000, with the majority arriving in Italy, according to the U.N. High Commissioner for Refugees. This month alone, more than 13,300 migrants have arrived — a number roughly equal to the first three months of the year combined.

The death toll has also jumped. Even before Sunday’s disaster, 950 migrants had died in the central Mediterranean this year, compared with only 50 during the same period last year, the U.N. refu­gee agency said.

On Monday, the ongoing crisis claimed new casualties even as the international effort to assess the extent of Sunday’s tragedy continued.

In Greece, at least three people died after a migrant vessel broke apart as it reached the island of Rhodes, with video footage showing desperate survivors clinging to floating debris.

Italy and Malta, meanwhile, were responding Monday to vessels in distress off the coast of Libya. An Italian coast guard official said 638 migrants found floating aboard six rubber rafts 35 miles off the Libyan coast were rescued.

[A private mission to save migrants]

At the same time, south of Sicily, three planes and seven ships continued scanning the Mediterranean for survivors and bodies from the boat that overturned Sunday, carrying between 700 and 950 passengers. Officials said it was unclear whether they would be able to resurface the vessel.

But the numbers of those recovered — 28 survivors and 24 bodies — remained unchanged from Sunday. The survivors were receiving medical treatment and were en route to Sicily with an expected arrival late Monday night local time, officials said.

Giovanni Salvi, the prosecutor in the Sicilian city of Catania, who interviewed a Bangladeshi survivor, said the cause of the wreck remained unclear. The boat’s Tunisian captain and a Syrian crew member were arrested and charged with favoring illegal immigration, an assistant prosecutor told the Associated Press. The captain was also charged with reckless multiple homicide, the official told the AP.

Italian coast guard officials, citing initial interviews with survivors, said earlier that the migrant ship overturned after a Portuguese vessel came to its aid and passengers rushed to one side to wave it down, tipping their boat over. But Salvi said authorities were also investigating whether the Portuguese ship, the King Jacob, accidently collided with the migrant ship.

A sweeping but costly Italian search-and-rescue program for migrants at sea ended in November, replaced with a more limited pan-European effort. But one problem, Salvi said, is that rescues are often now carried out by commercial vessels that are not necessarily prepared for such missions.

“Rescues at sea require high training,” he told reporters in Catania.

[Amid flood of refugees to Europe, Italy opens a back door]

The survivor, Salvi said, told officials that as many as 950 passengers were onboard the three-level boat. Hundreds had been locked in a hold, he said, and appeared to have perished when the boat sank. Salvi cautioned that other survivors had said roughly 700 were on board.

Italian Prime Minister Matteo Renzi called Monday for a more aggressive effort by Europe and other nations to address the destabilization in Libya. But he ruled out any immediate military action, a step Italy has been weighing in recent months.

“Right now a military land intervention of an international force in Libya represents an absolutely excessive risk,” he told RTL radio. “We can’t consider sending tens of thousands of men without a strategy, with an emotional approach. I’m ruling out the possibility of boots on the ground, right now.”

Faiola reported from Berlin. Stephanie Kirchner in Berlin, Stefano Pitrelli in Treviso, Italy, and Brian Murphy in Washington contributed to this report.

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