CNN has also obtained an al Qaeda document that spells out the terrorist group's plan to separate Spain from the U.S.-led coalition on Iraq.
The document was published on the main message board that is used by al Qaeda and its sympathizers last December.
The strategy spelled out in the document calls for using terrorist attacks to oust Prime Minister Jose Maria Aznar's Partido Popular from power and replace it with the Socialists.
That, in turn, was expected to drive a wedge between Washington and Madrid and result in the withdrawal of Spanish military forces from Iraq.
"We think the Spanish government will not stand more than two blows, or three at the most, before it will be forced to withdraw because of the public pressure on it," the al Qaeda document says.
"If its forces remain after these blows, the victory of the Socialist Party will be almost guaranteed -- and the withdrawal of Spanish forces will be on its campaign manifesto."
In technical parlance, they cannot be deterred.
