The UN's International Organization for Migration said delays in state-led search and rescue (SAR) operations played a part in several fatal incidents in the perilous sea crossing from north Africa.
And the IOM said the 441 known deaths in the first three months of the year was likely an undercount of the true number.
"The persisting humanitarian crisis in the central Mediterranean is intolerable," said IOM chief Antonio Vitorino.
"With more than 20,000 deaths recorded on this route since 2014, I fear that these deaths have been normalised. States must respond," he added.
The IOM said delays in rescues were a factor in at least six incidents so far this year, leading to the deaths of at least 127 people.
"The complete absence of response to a seventh case claimed the lives of at least 73 migrants," it said in a statement, adding that non-governmental organisations' SAR efforts have markedly diminished in recent months.
The UN agency's Missing Migrants Project is also investigating several cases in which boats were reported missing, where there are no records of survivors, no remains and no SAR operations.
The fates of more than 300 people aboard those vessels remain unclear, the organisation said.
The IOM said that over the Easter weekend, 3,000 more migrants reached Italy.
Numbers of boat landings have surged this year, with almost 32,000 migrants arriving on Italy’s shores since January, according to interior ministry figures, compared to 8,000 over the same period in 2022.
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