"The persisting humanitarian crisis in the central Mediterranean is intolerable," said UN International Organization for Migration (IOM) chief Antonio Vitorino.
"With more than 20,000 deaths recorded on this route since 2014, I fear that these deaths have been normalized," he warned.
"States must respond. Delays and gaps in state-led SAR are costing human lives."
The IOM said delays in state-led search and rescue (SAR) operations were a factor in several fatal incidents in the perilous 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 IOM said delays in such 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 organizations' search and rescue efforts have markedly diminished in recent months.
"Over the Easter weekend, 3,000 migrants reached Italy, bringing the total number of arrivals so far this year to 31,192 people," the IOM said.
The UN agency's Missing Migrants Project is also investigating several reports of cases in which boats are 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 organization said.
"Saving lives at sea is a legal obligation for states," said Vitorino.
"We need to see proactive state-led coordination in search and rescue efforts. Guided by the spirit of responsibility-sharing and solidarity, we call on states to work together and work to reduce loss of life along migration routes."