African immigrants arrive in a fishing boat carrying 60 to the port of Los Cristianos, in the Canary island of Tenerife, Spain, 1 Feb 2007

The fate of the migrants, who are believed to be Pakistanis, has been in question since Saturday, when a Spanish rescue ship intercepted the boat, and attempted to bring it to the northern Mauritanian port, Nouadhibou.

Mauritanian officials refused to allow the migrants ashore, saying the boat originated from a country further south.

Mauritanian journalist Salem Bokari says the interpretation of a repatriation agreement has been at issue.

"There is an agreement with Mauritania and Spain, but only regarding the migrants who leave Mauritanian ports," said Bokari.

Spanish officials said Mauritania was obliged to accept the migrants' boat because it was in distress.

The European Union stepped up joint patrols of the Senegalese and Mauritanian coastlines in recent months to catch would-be migrants at sea.

Tens-of-thousands of migrants have embarked on the sea journey up the coast of Africa to Spain's Canary Islands during the past year, hoping to slip into the European Union. More than 31,000 reached the islands last year.

Many of them are from African countries, but some Asian immigrants also attempt to make the crossing.

The trip can be dangerous. Migrants make the trip in wooden fishing boats, and risk dying from hunger, dehydration or falling overboard in high seas.