The bodies of 28 illegal West African migrants have been found washed up on a beach in Western Sahara
They had set off in two boats from Morocco in an attempt to reach the Spanish Canary Islands, it said.
Meanwhile, Spanish authorities said on Tuesday 172 more migrants had arrived in the Canaries.
About 12,000 migrants have made the voyage to the Canaries this year, more than twice the 2005 total, Spain says.
The long and dangerous trip to the islands has become a favoured route in recent months after Spain and Morocco stepped up joint efforts to prevent immigration by sea across the much shorter Strait of Gibraltar.
The migrants' bodies were discovered in Blibilatte, 40km (25 miles) north of the territory's chief city Laayoune, according to local officials.
A search was under way for other passengers on board the boats. Police carrying out the search have already detained 49 people.
In similar incidents on Tuesday, 96 migrants made it ashore at Los Cristianos on Tenerife, with another 76 reaching the small island of El Hierro after 11 days at sea.
On Sunday, sympathetic sunbathers holidaying on Tenerife rushed to give assistance after three makeshift boats carrying 205 exhausted Africans reached the shore.
Bodies of 28 migrants wash up on Saharan coast