Two overcrowded dinghies capsized in the Strait of Sicily between Italy and Libya, the International Organization for Migration (IOM) and the UN refugee agency UNHCR said, Reuters reported.
"Those two incidents together appear to be the numbers that would bring this year's total to 5,000 (deaths), which is a new high in this crisis," IOM spokesman Joel Millman told a Geneva briefing.
"This is the worst annual death toll ever seen," said UNHCR spokesman William Spindler.
Some 3,777 migrants perished at sea during all of 2015, the IOM said.
The UNHCR appealed to states to open up more legal pathways for admitting refugees.