Most of those on board are thought to have been Pakistanis, who have been taking more and more places on migrant boats.
Olivia Headon, from the International Organisation for Migration, said most of those on board were Pakistanis.
"They have given an estimate of 90 who drowned during the capsize, but we still have to verify the exact number of people who lost their lives during the tragedy," she said.
The bodies of two Libyans and eight Pakistanis are reported to have washed up on Libyan shores, while three people are thought to have survived, she added.
Security officials in the western Libyan town of Zurawa said two Libyans and one Pakistani had been rescued.
She added that Pakistani nationals had been taking an increasingly large share of migrants trying to cross the Mediterranean via Libya to Europe.
Zurawa - near Libya's border with Tunisia - is often the site of migrant boat departures.
The numbers of people trying to reach Europe from Libya has dropped sharply since July.
Libyan authorities have blocked departures after pressure was applied by Italy and the European Union.
Over the last four years, more than 600,000 people are believed to have made the journey from Libya to Italy.