PARIS - THE suspected military chief of the Basque militant group ETA, Garikoitz Aspiazu, alias Txeroki, was arrested overnight in the French Pyrenees, French Interior Minister Michele Alliot-Marie said on Monday in a statement.

She did not provide any details regarding the arrest, but said Txeroki is suspected of being the perpetrator' of the murder of two Spanish police officers in southern France last December.

The arrest is the biggest blow against ETA since the group's presumed leader, Javier Lopez Pena, was detained along with three other suspected members of the group in France in May.

The Basque news agency Vasco Press said police arrested Txeroki along with a woman also suspected of being an ETA member at a place where they were staying at 3:30am in the town of Cauterets following a joint investigation by French and Spanish police.

Earlier this month Spanish Interior Minister Alfredo Perez Rubalcaba said two recently detained suspected ETA members claimed that Txeroki had told them that he had 'direct participation' in the shooting of the two officers in Capbreton on December 1, 2007.

One of the two suspected ETA members said he 'heard Txeroki recognise that he was the assassin of the two policemen', the minister added.

The two plain-clothed policemen, Raul Centeno, 24, and Fernando Trapero, 23, had been taking part in a surveillance operation with French police in southwestern France when they were shot outside of a cafeteria.

French police detained two suspected members of an ETA commando who are believed to have taken part in the attack several days later in the southern Lozere region while a third suspect remained at large.

Some Spanish media outlets had already raised the possibility that the third person who took part in the shooting was Txeroki.

ETA, which has killed over 820 people in its 40-year campaign for an independent Basque homeland, claimed responsibility for the attack in a statement issued on December 17, saying it would strike Spanish security forces 'wherever they may be'.

France has helped Spain in its clampdown on ETA after the group called off a 15-month-old ceasefire in June 2007, shattering hopes of a peace settlement, arresting a number of ETA militants.

Vasco Press said Txeroki has been the reputed head of ETA military operations for the past five years, and as such was responsible for ordering and planning its bomb attacks.

An ETA hardliner, Txeroki is suspected of torpedoing the peace talks by ordering the December 30, 2006 bombing of a Madrid airport car park that killed two people.

Mrs Alliot-Marie praised the arrest of one of the most hunted men in Europe as an example of the excellent cooperation of French and Spanish police.

'This arrest demonstrates once again the resolute engagement of the French police and gendarmes to combat all forms of terrorism,' she said in the statement.

'It illustrates once again the excellent collaboration between France and Spain against Basque terrorism'.