MADRID (AP) — The bodies of four women have been found in a rubber-dinghy boat off the coast of southeast Spain, authorities said Friday.

The government office in the southeast city of Murcia said the boat was towed by marine rescue services to the port of Cartagena early Friday after being spotted by coast guards.

It said the women appeared to be of North African origin and may have been migrants trying to reach Spain. Migrants regularly use such boats to reach Spain from northwest Africa.

Autopsies are to be held to establish the cause of death, the office said.

No other occupants were found in the boat and it was not immediately known if there had been any beforehand.

Tens of thousands of migrants from sub-Saharan countries fleeing poverty, conflict and instability in West Africa try to reach Spain each year by boat. Most go in large open vessels to the Canary Islands in the Atlantic, while others from Morocco, Algeria and Middle Eastern countries try to cross the Mediterranean Sea and Atlantic Ocean to mainland Spain. Several thousand die making the hazardous journey.

The Interior Ministry says 15, 351 migrants arrived in Spain by boat between Jan. 1 and Mar. 31, up by more than 4,000 in the same period last year. The vast majority arrived on the Canary Island route.