The Spanish royal family
Princess Sofia, Princess Leonor, Princess of Asturias, King Felipe VI of Spain and Queen Letizia of Spain at their coronation in Madrid in June 2014AFP/Getty

Islamic State (Isis) jihadists plotted to attack Spain's royal family, according to Spanish authorities following raids on alleged terror cells last week.

Spain's Interior Minister Jorge Fernandez Diaz said on 17 March that handwritten notes had been found in the possession of the ringleader of the groups, which contained specific threats against Spanish King Felipe VI's daughters Leonor, nine, and Sofia, seven.

"Felipe of Spain will know what suffering is when his two daughters are under the rubble," the note said according to statements filed before magistrate Javier Gómez Bermúdez at the National Court, Spain's La Razon reported.

Eight people were arrested in coordinated anti-terror raids across Spain last week, with seven remanded in custody on Sunday (15 March).

Six men and two women were taken into custody after raids in Barcelona and Girona in the north east, and Avila and Ciudad Real in central Spain.

In a statement, Spanish police said that the group had been in contact with an IS operative, who was directing their activity from Syria and Iraq.

The group was described in the statement as a "propaganda machine" that was targeting immigrants and Spaniards of Moroccan origin.

"The text is very unpleasant and shows the extent of radicalisation of these people," prosecutors told the newspaper.

It is believed that approximately 100 Spanish citizens have travelled to Iraq and Syria to join IS.