Spain is on full alert in case of a new attack by ETA in the wake of the arrest of the Basque separatist organisation`s alleged military chief, Interior Minister Alfredo Perez Rubalcar said Wednesday.

`It must be expected,` he said on Cadena Sur radio. `ETA will try to convince us that it is not so weakened` following the arrest in France on Monday of Miguel de Garikoitz Aspiazu Rubina.

Rubalcar said that ETA`s leadership also wanted to counter a growing feeling of weakness among the group`s activists and supporters following a string of arrests of its top figures.

Known by the nom de guerre `Txeroki` -- Basque for Cherokee -- the suspected Basque separatist activist was captured on Monday in a pre-dawn raid on a rented apartment in the French Pyrennean spa resort of Cauterets.

Spanish officials describe Txeroki as the most important ETA leader still at large and the head of the group`s armed wing.

He is accused, in particular, of the murder of two Spanish officers in France last December. According to one media report they were working with French officers to track and capture him.

The 35-year old militant was arrested with alleged fellow ETA member Leire Lopez, according to investigators.

Rubalcar said his arrest would be seen as a turning point in the group`s history, as Txeroki carried great political weight within ETA and was a legend among Basque separatists.

`But I would not say that this means the end` for ETA, which is held responsible for the death of 824 people in a 40-year armed campaign for independence of the Basque country.

The minister said he had reliable information on who might succeed `Txeroki`, but did not reveal any names.