Four persons believed to be members of the Basque separatist group ETA have been arrested Saturday in south-west France, the Spanish Interior Ministry said.

French and Spanish security forces carried out an operation in a suburb of Cahors, a town located near Toulouse and detained three men and a woman who are believed to be involved in the deadly attack which occurred last year at the Madrid airport.

Spanish Interior Minister Alfredo Perez Rubalcaba said the suspected terrorists were planning a new attack and had already manufactured a car bomb when special forces raided their house early Saturday.

Perez Rubalcaba said they were armed and possessed explosives, but didn’t resist the arrest. One of the men was identified as Jose Luis Iruretagoyena Lanz and according to investigators he is one of the top ETA members specialized in the use of explosives.

Ander Mugica Alaitz Aramendi, Alaitz Aramendi Jaunarena and Ohian Barandalla were the three other persons arrested, the Spanish official added. The group is allegedly involved in another failed attack that occurred earlier this month in northern Spain.

ETA or “Basque Homeland and Freedom” has been labeled as a terrorist organization by the European Union, United Nations and the United States for its armed campaign launched four decades ago in northern Spain and southern France.

The group is militating for an independent Basque state, but encountered the firm opposition of Spain, France and the European Union.

Also on Saturday, media reports said the leading member of the Basque Nationalist Party (PNV) and head of Spain's Basque Country autonomous community, Juan Jose Ibarretxe is reportedly preparing a new referendum on the region’s independence.