Morocco's navy on Saturday found the bodies of 15 migrants from sub-Saharan Africa on board a boat stranded at sea for days and rescued 53 survivors, a military source said.

Coastguards recovered "15 lifeless corpses" from the vessel in the Mediterranean Sea after it was left drifting for four days following engine failure on its way to Spain, the source said.

The 53 other survivors on board, including eight women, were taken to the port of Nador.

Increasing numbers of Moroccans and sub-Saharan migrants are seeking to enter Spain, either by sea or by smuggling themselves into the Spanish enclaves of Ceuta and Melilla, which are in Morocco and are the only European territories in Africa.

The International Organization for Migration says that some 51,000 migrants have arrived in Spain by sea this year, and that over 630 have died or gone missing trying.

On Friday the Moroccan navy said it rescued 289 migrants, mostly from sub-Saharan African off Nador.

Moroccan authorities say that between January and the end of September they stopped some 68,000 illegal attempts to cross into Europe and took down 122 people smuggling gangs.