MADRID : Families of the crew of a Spanish tuna trawler being held by Somali pirates appealed to Spain's government on Friday to negotiate with the kidnappers, who have threatened to kill the hostages.

They urged Spanish authorities to release two suspected Somali pirates being held in Spain, as demanded by the kidnappers.

Ricardo Blach, the skipper of the boat, the Alakrana, and one of the 36 hostages, told Spanish media on Thursday that the pirates had threatened to kill three of them in three days unless their demands were met.

The pirates on Thursday moved the three onshore from the boat off the coast of Somalia.

"They have just told us that if in three days there is no change over the two held in Spain, they will kill the three and then three others and then more," Blach told the newspaper El Pais by satellite phone.

The crew are enduring difficult conditions with "little drinking water or food," Argi Galbarriatu, the sister of one of the crew members, told a news conference in the port of Bermeo, in Spain's northern Basque Country, where the Alakrana is based.

In a joint statement, the families urged Spanish authorities to "act immediately" and "do everything possible to bring home the 36 fishermen."

"We demand that all the parties work in the same direction" and that the Spanish government opts for "negotiation" rather than putting the life of the crew in danger with military action, said Maria Angeles Jimenez, the wife of another of the crew.

The pirates, who seized the boat on October 2, are demanding four million dollars (2.6 million euros) ransom as well as the release of the two suspected pirates who are facing trial in Spain.

Spanish troops monitoring the area off the Somali coast captured the two suspects shortly after they left the Alakrana on a small boat.

Spain's secretary of state for defence, Constantino Mendez, Friday reaffirmed that the two suspects would not be released, and "that is not negotiable."

He told Spanish National Radio that the crew are "in good health" and that the pirates are "dramatising" the situation in a "negotiating tactic."

Two Spanish frigates remain on watch off Somalia.

- AFP /ls