The UN's refugee agency (UNHCR) also updated its toll on Tuesday to 880 from 700 provided on Sunday. Both the IOM and UNHCR tallies are based on accounts taken from survivors in Italy in recent days.
The IOM said that 62 were confirmed dead while 971 were missing.
Some 700 are thought to have drowned in three boat wrecks between Wednesday and Friday last week, while others are feared dead in six smaller wrecks.
Among the victims were at least 40 children.
Photo: Gabriel Bouys/AFP
A photo of a drowned migrant baby, in the arms of a German rescuer, was published by a charity on Monday with the aim of force European leaders to grant migrants safe passage.
The baby in the photograph was not identified, but the German non-governmental organization Sea-Watch said the infant was found in the water last week after a wooden boat carrying 350 migrants capsized off the Libyan coast as it tried to make its way to Europe.
Meanwhile, a nine month old baby was orphaned after her mother, who was pregnant with her second child, died.
And a 13-year-old from Eritrea told aid organizations that he saw his mother and 11-year-old sister die.
Over 1,700 migrants are feared to have drowned as they attempted to reach Italy so far this year, and at least 1,782 died during the same period in 2015.
A joint report published by Europol and Interpol this month said there were around 800,000 migrants in Libya waiting to attempt the journey across the Mediterranean.