At least 44 migrants drowned on Sunday when their boat capsized off the coast of the Western Sahara, migrant aid agency Caminando Fronteras said.
Twelve others survived the tragedy, which happened when the boat sunk off the coast of Cap Boujdour, the agency's Helena Maleno tweeted.
The survivors were arrested, Maleno wrote.
The bodies of seven victims were brought back to shore but the others could not be retrieved, she added.
It was not clear where the boat was heading, but usually migrants leaving from that area try to reach Spain's Canary Islands.
Morocco is a key transit point on routes taken by migrants hoping for better lives in Europe.
On Friday, Morocco and Spain said in a joint statement they were committed to strengthening cooperation on irregular migration.
More than 14,700 attempted irregular departures were prevented and 52 human smuggling networks broken up in Morocco during the first three months of this year, according to interior ministry figures.
Moroccan authorities stopped more than 63,120 crossings last year and shut down 256 smuggling networks.
According to the Spanish interior ministry, more than 40,000 migrants arrived in the country by sea in 2021.
That same year, according to Caminando Fronteras, 4,404 migrants died or went missing as they tried to reach Spain.
Text initially published on: France 24