Story highlights Mikel Irastorza is detained in a joint French-Spanish operation in southwestern France

Spanish authorities allege he is the leader of Basque separatist group ETA

(CNN) Security forces have arrested the alleged leader of the Basque separatist group ETA, Spain's interior ministry said, in what is described as a "hard blow" to the militant organization.

Mikel Irastorza, 41, was detained Saturday in the town of Ascain, near the border with Spain in southwestern France, in a joint French-Spanish operation, the interior ministry statement said.

Irastorza, who had been on the run since 2008, had been in charge of ETA activities for the past year and was the most senior ETA member still at large, the ministry said, following the arrest of the group's previous leader.

His arrest represents a "hard blow" to ETA, it said, "because it involves a leadership loss within the organization and the elimination of its management structure, which was responsible for administering the weapons and the explosive arsenal."

Two other people were arrested with Irastorza, the statement said. They're accused of collaboration with ETA and giving shelter to Irastorza in their house, the statement added.

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