Eight more suspected Basque militants were detained in France and in the Spanish city of San Sebastian yesterday in connection with the suspected plot, which may have embroiled at least four members of the same family.
The Spanish Interior Minister, Juan Alberto Belloch, said the suspects were definitely plotting to kill the King. "The information arising from the arrests, taken together, allows us to say that the main objective of this Eta command was to carry out an attack on the King," he told a news conference in Madrid.
The national police chief, Angel Olivares, said yesterday in the Majorcan capital, Palma, that weapons, including three machine guns, several pistols, a rifle with telescopic sight, 3lb of explosives and an explosive device, had been seized, along with documents.
Two of the men were seized in a flat they had rented 500 yards from the Spanish royal family's summer palace, Marivent, just outside Palma. The third was detained on board a yacht, La Belle Poule, in the north-eastern port of Alcudia. The King has been in Majorca with Queen Sophia and other members of the royal family since mid-July.
The Secretary of State at the Interior Ministry, Margarita Robles, said yesterday that it was "a credible hypothesis" that the three men, including a father and son, were planning to assassinate King Juan Carlos or some senior member of the royal family. The three had sailed in their rented yacht from Nice on 14 July and arrived in Alcudia on 17 July. Tipped off by the French, the Spanish police had kept an eye on them from the moment they entered Majorcan waters.
Of those detained, Juan Jose Rego Vidal, 53, Spanish-born but with French nationality, has apparently been an Eta member since 1973.
The other two were his son, Inaki, and Jorge Garcia Sertucha. Mr Rego senior served a year's imprisonment in 1979 for preparing a previous attack on the King, and on the former Prime Minister, Adolfo Suarez. He was also implicated in a plot against the King's late father, the Count of Barcelona, in 1975.
Following Wednesday night's police swoop in Majorca, seven more people were detained yesterday in France, and one in San Sebastian. They included Juan Jose Rego's wife, their daughter and her boyfriend, and four suspected Eta members in hiding in France.
Ms Robles hailed the police operation as a success that demonstrated the effective co-operation between France and Spain in countering Basque extremism.