Counter-terrorism forces in the country have warned about an "increase in allusions to our country" in recent texts, videos and propaganda produced by ISIS.
The terrorists have been increasingly writing in Spanish and even analysing Spain's election results, which authorities believe "increases the possibility of a terror attack in our territory".
A statement written in Arabic in July by the ISIS-linked Wafa Media Foundation said: "Anywhere you consider a valid target to punish Spanish criminals, by any means."
The group also urged people living in the north African area of Maghreb - Morocco, Tunisia, Mauritania and Libya - to attack Spanish citizens.
Spanish ISIS researchers said they have seen a worrying rise in references to Spain by jihadis.
They said more texts and statements are being translated into Spanish which "give our country more propaganda relevance and increase the possibility of terror attacks in Spanish territory".
More and more terrorists are speaking Spanish, they added.
With propaganda being one of the terror group's most powerful weapons, Spanish authorities are becoming increasingly concerned.
The researchers said it has become more common over the past few months to find ISIS videos subtitled "entirely or solely" in Spanish.
One 14 minute video, called "The path of the righteous parents", is subtitled in Spanish and focuses on attracting new recruits.
The messages are broadcast from different areas of ISIS-held territory, meaning "differing people follow specific guidelines of a central organisation", experts said.
And the Spanish flag has also appeared in pictures entitled: "A religion, a caliphate."
The photo features a terror waving a black ISIS flag as they stamp on a Spanish one with 11 other extremists.
Concerningly, researchers said the information is being disseminated in a "more than correct Spanish".
Spanish counter-terrorism sources said they suspect some of the propaganda material may be written by Spanish citizens.
They believe their aim is to encourage "lone wolves, frustrated by the inability to travel to Syria and Iraq to fight alongside terrorists and to carry out attacks in their country of origin or residence", Express reported.
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