Spanish police have confirmed that they are on high alert over an possible attack ahead of Real Madrid's Champions League clash with Manchester City on Tuesday night, after Islamic State issued a chilling threat to all four Champions League quarter-finals.

On Monday ISIS launched a threat against all four stadiums hosting quarter-final matches this week, including Arsenal's Emirates Stadium and Real Madrid's Santiago Bernabeu. 
 
The Al Azaim Foundation, the outlet which is often responsible for spreading messages from ISIS, published a chilling poster with the message 'Kill them all' alongside the names of all four stadiums hosting the matches. That has prompted beefed up security in the Spanish capital, where two of the games are being played.