But silencing those who oppose Basque independence is clearly part of the separatists' strategy.
The government blames the rebels for causing 800 deaths in their 31-year struggle for Basque independence.
Mr. Zapatero has said that Basque independence is off the table.
The referendum call was widely seen as a veiled attempt to garner support for Basque independence.
Most of the kidnappings ended with ransom payments that went to pay for the group's long and violent struggle for Basque independence.
The Government appeared to interpret the statement as as tacit support for Basque independence.
More than 700 people have been killed since the group started its armed struggle for Basque independence in 1968.
Founded in 1959, it evolved from a group advocating traditional cultural ways to a paramilitary group with the goal of Basque independence.
The lull had raised hopes that the 20-year campaign for Basque independence was nearing its end.
López is known for his opposition to Basque independence.