Spain's government has warned against the threats amid the latest signs that the terror group has encouraged sympathisers to launch attacks.
ISIS has reportedly vowed to take revenge on Spain after anti-terror police arrested dozens of suspected militants in 2016.
Authorities have seen an alarming increase in the number of propaganda videos subtitled in Spanish and aimed at possible recruits from Spain.
The warning comes after a number of attacks claimed by ISIS - including attacks on a Christmas market in Berlin and Bastille Day fireworks in Nice, France, last year.
Holidaymakers have expressed fears of beach attacks in Europe amid threats from terrorists and following a deadly attack in Tunisia.
ISIS fanatic Seifeddine Rezgui killed 38 people, including 30 British tourists, in a mass shooting in June 2015.