Garikoitz Aspiazu, alias Txeroki, was detained early on Monday morning, Michelle Alliot-Marie said in a statement, without giving further details of the arrest.

"Txeroki is suspected of being the perpetrator" of the murder of two Spanish police officers in southern France last December, she said.

Eta has been waging a 40-year campaign for an independent homeland in Spain and southern France for the Basque people. The group has killed more than 820 people.

Police killed

Txeroki's arrest comes six months after Javier Lopez Pena, Eta's presumed leader, was detained, along with three other suspected members of the group, in France in May.

Spanish media said Txeroki was arrested with a woman in the town of Cauterets, citing sources within anti-terrorism police.

The Spanish police officers who were killed last December had been on a surveillance operation with French police in southwestern France.

Eta claimed responsibility for the attack, saying it would attack Spanish security forces "wherever they may be".

French police later arrested two suspected Eta members in the southern Lozere region, while a third suspect remained at large.

Before news of the arrest of Txeroki, Spanish media had speculated that he was the third suspect.

France has helped Spain in its operations against Eta after the group ended a 15-month-old ceasefire in June 2007.

Agencies