MADRID  Pirates on Friday threatened to kill three crew members of a Spanish fishing ship they seized over a month ago if two suspected pirates being held in Spain were not freed, according to news agencies who quoted the captain of the vessel.

“They have taken three of our crew and have given a deadline of two days,” the captain, Ricardo Blach, told Spanish television by telephone from the ship. “If in two days there are no signs that those two Somalis are being sent back here, they are going to kill them and immediately take another three hostages. This is a lottery,” he said, according to the reports.

Crew members of the ship, the Alakrana, had pleaded with their relatives on Thursday to press the Spanish government to do more to gain their release.

The relatives said that during telephone calls placed from the Alakrana, a 100-meter tuna-fishing vessel held off the Somali coast, captives briefly described their plight and said the pirates had followed through on their threat to start taking captives ashore. There are 16 Spaniards among a crew of 36.