Eleven lifeless bodies were recovered on Monday off the Spanish island of Cabrera in the Balearic Islands, the region's prefecture announced.
Authorities said that three people had been rescued and 11 bodies recovered after a sailboat was reported west of Cabrera.
The authorities, who gave very few details at the moment, were not in a position to confirm that the bodies were those of migrants.
But the number of arrivals of migrants, often from Algeria, on the archipelago or in south-eastern Spain has soared in recent months. Nearly 300 of them were rescued between Monday and Friday off the Balearic Islands.
While controls have been tightened in the Strait of Gibraltar, which separates Spain from Morocco, the migratory route of the "harragas", the Arabic nickname given to illegal migrants leaving from Algeria, has increased, according to NGOs and the authorities.
It can be more than 200 km long and is more dangerous at this time of year, as the sea is much less favourable than in summer.
Women and children
In mid-September, the bodies of eight migrants from Algeria or Morocco, including a child and three women, were found by Spanish authorities on the beaches of Almeria province, in the south-east of the peninsula.
Last week, a pregnant Algerian woman and her five children were rescued off the coast of Alicante province (south-east), further north.
Several NGOs receiving migrants on Spain's eastern and southern coasts have recently reported an increase in the proportion of women and minors.
For these migrants, Spain is only a stopover, their final goal being usually France.
A total of 13,320 migrants arrived on the Spanish mainland or Balearic coasts between January and the end of September, 2,104 (19%) more than in the same period last year, according to the latest figures from the Ministry of Interior.
A further 13,118 reached the Canary Islands, off the coast of Africa, more than double the 6,124 who arrived in the same period in 2020.
According to the International Organisation for Migration (IOM), 2021 is "the deadliest year on the migration route to Spain" with at least 1,025 people dying in their attempt to reach the Spanish mainland, the Canary Islands or the Balearic Islands.
The route to the Canary Islands in the Atlantic Ocean is particularly deadly. At least 785 people died trying to reach the archipelago from West Africa between January and August 2021, according to IOM.
The NGO Caminando Fronteras, which relies on the testimonies of migrants or their families, estimates that more than 2,000 people died or disappeared while trying to reach the Canaries in 2021.