(Adds details about migrants aboard, paragraphs 5-12)

By Ibrahima Sylla

NOUAKCHOTT, Feb 8 (Reuters) - Mauritania faced growing international pressure on Thursday to allow at least 400 Asian and African migrants aboard a stranded freighter off its coast to disembark, as concerns grew over their health and safety.

Mauritania has refused to accept the Marine 1, which is believed to have set sail from Guinea on its way to Spain's Canary Islands. The ship sent out an SOS signal after its motors broke down in international waters off Senegal on Feb. 2.

It was intercepted the following day by a Spanish coastguard vessel which towed the freighter to its position off Mauritania's northern fishing port of Nouadhibou.

Representatives of the Mauritanian Red Crescent, Spanish Red Cross and International Organisation for Migration (IOM) travelled by boat to the stranded vessel on Thursday.

They delivered five tonnes of drinking water, food and humanitarian supplies but were unable to board the 50-metre vessel, because high seas made this dangerous.

Its occupants told them by radio there were more than 400 people on board, some suffering from sea-sickness and diarrhea.

"They said they wanted to go on land," Michael Tschanz, the IOM representative in Mauritania told Reuters by mobile phone.

"It seems the majority of them are not Africans, but Asians. They say 305 of them are from Kashmir and present themselves as people who would be eligible for refugee status," he added.

Others on board apparently came from Myanmar, Sri Lanka, Ivory Coast, Sierra Leone and Liberia, and some said they had been on board for more than two months.

"Our understanding is that this boat has been going along the coast of Africa," Tschanz said.

During the visit, two people jumped overboard from the migrant ship and were picked up by a Mauritanian patrol boat.

"That seems like a sign of despair," Tschanz said.

HUMANITARIAN APPEAL

Spain, which is on the front line of Europe's efforts to stem an influx of illegal job-seekers, has been lobbying Mauritania to take responsibility for the stranded migrants.

Madrid has also asked Senegal and Guinea whether they would be willing to allow them ashore.

The U.N. refugee agency UNHCR on Thursday added its voice to calls for the freighter to be allowed to enter a safe port.

"At this point in time, the main priority should be to help these people and not let them drift on the high seas in precarious conditions," George Okoth-Obbo, UNHCR Director for Protection, said in a statement from Geneva.

The IOM, which handles migration issues worldwide, was offering to help organise repatriation flights for the stranded migrants when they eventually came ashore, said Laurent de Boeck, a spokesman for the organisation in Dakar.

But he made clear the IOM's policy was to support a voluntary return home by the migrants, not forced repatriation.

The ship has become a test case for Spain, which launched a diplomatic offensive in West Africa last year in a bid to stem soaring illegal migration from the poverty-stricken region to the Canaries.

Madrid has been offering increased aid in return for help halting clandestine migration. (Additional reporting by Andrew Hay in Madrid and Pascal Fletcher in Dakar)

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