An average of six migrants died crossing the Mediterranean every day last year, a UN report says.An estimated 2,275 people died making the journey in 2018.
The death toll was particularly high on the route to Spain, where it was more than four times the 2017 figure.
Italy had earlier highlighted the lower overall number of deaths last year, due to fewer people making the crossing.
But the rate of deaths from Libya rose to one for every 14 arrivals in 2018 – from one in 38 the year before.
This latest report from the UN refugee agency (UNHCR) highlighted the higher rate of deaths among those who did make the journey, pointing to the difficulties faces by humanitarian rescue groups as the cause.
"Although the overall number of deaths at sea in the Central Mediterranean more than halved in 2018 compared to the previous year, the rate of deaths per number of people attempting the journey rose sharply," it said. "It is likely that reductions to search and rescue capacity coupled with an uncoordinated and unpredictable response to disembarkation led to an increased death rate," the report said.
Italy's refusal to accept migrants rescued off the Libyan coast coincided with reduced search and rescue operations from European ships - and there had been a rise in "interceptions" by the Libyan Coast Guard instead. But the report said those people were then transferred to detention centres, where they faced "appalling" conditions.
"Detainees in some facilities were given limited access to food, while there were also reports of an outbreak of tuberculosis," it said.
For those who were rescued by European ships, it criticised the lack of a coordinated response on their fate.
"On several occasions, large numbers of often traumatised and sick people were kept at sea for days before permission to disembark was granted," it said.