Police in Spain and France claim to have destroyed ETA's logistics structure after a series of raids in south-west France at the weekend.
It was the first major operation by France's special Search and Intervention Brigade (BRI), established last June to collaborate with Spanish police in their fight against the Basque terrorists.
The most important arrest was that of Mr Asier Oiartzabal, alias Baltza, who is alleged to have been responsible for ETA's logistical structure. Four other alleged terrorists, two men and two women, were detained in the same operation. The latest detentions bring to 100 the number of terrorist suspects held on both sides of the border since the beginning of the year. Mr Oiartzabal was armed with a pistol when police raided his house in Dax, where he was accompanied by the two women. The two other men were detained as they attempted to escape on the nearby motorway.
In the same building police found the plans of a mining complex in Savoy, weapons and ammunition, cash to the value of 25 million pesetas (€155,000) and one million French francs, false identity papers and other documents.
The Spanish interior minister, Mr Mariano Rajoy, yesterday described the operation as "very important". He said that all the signs suggested that the gang was planning to steal up to three tonnes of dynamite.
Police sources believe ETA is in urgent need of new supplies of explosives, having used up much of the 1,600 kilograms of dynamite stolen in an earlier raid on another mining store in Grenoble last March.
In 1999, during ETA's 15-month ceasefire, they stole more than eight tonnes of dynamite from a mine in Brittany, a quantity of which was later recovered by police and the remainder used in other attacks. Oiartzabal is also alleged to have taken part in the Brittany operation.
Police described Oiartzabal (30) as one of the new generation of ETA terrorists who began his career in the kale barroka (street violence) of Basque towns. He was arrested for the first time in 1993 and charged with public disorder. He has been in exile in France for several years during which time police say he has risen through the ranks of the organisation. However, he is believed by the authorities to have crossed into Spain on several occasions to take part in terrorist acts. They say he became logistics chief 12 months ago after Inaki de Renteria, the former leader, was arrested in another important anti-terrorist operation.
The attacks in the US that shook the world's travel industry have seen Spanish hotel sales plummet and could result in major tourism companies missing their earnings targets, officials said on Monday.
"Since September 11th travel-agency sales are down about 25 per cent compared with the same time last year, mainly due to falls in our main British and German markets," Felipe Gaspar, secretary general of Zontur told Reuters. Members of Zontur employ 140,000 people in 3,000 establishments and provide accommodation to 11 million tourists a year in Spanish resorts.
Global tourism experts have said the industry is currently facing its worst crisis since the Gulf War in 1991.