EUROPE is on guard following ISIS's threat towards the four stadiums hosting Champions League quarter-final matches this week - including the Emirates Stadium in London.
The Islamic State revealed a sinister poster on Monday night that included the names of the four high-capacity venues and a message that read: "Kill them all".
Arsenal host Bayern Munich tonight as Manchester City travel to face Real Madrid, while Wednesday sees Atletico Madrid play Borussia Dortmund and Paris Saint-Germain welcome Barcelona.
Arsenal's Emirates Stadium, Real's Santiago Bernabeu, Atletico's Metropolitano Stadium and PSG's Parc de Princes are all on high alert.
The Met Police said today they have a "robust policing plan" for Arsenal's match against Bayern Munich.
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They said the UK terrorism threat level remains at 'substantial' meaning an attack is likely.
Arsenal have also released a statement, saying tonight's fixture will be "no different" from normal.
The club said: “We work closely with the Metropolitan Police regarding the safety and security of all supporters and staff at Emirates Stadium for all our matches."
It comes amid fears of a resurgent ISIS after the group killed more than 140 people in a terrorist attack in Moscow last month.
The death cult appears to be rising again as chaos spills out from the Middle East.
But despite the threats, UEFA have confirmed that this week’s Champions League matches will take place as planned.
A statement issued on Tuesday read: “Uefa is aware of alleged terrorist threats made towards this week’s Uefa Champions League matches and is closely liaising with the authorities at the respective venues.
“All matches are planned to go ahead as scheduled with appropriate security arrangements in place.”
Spain has already activated "all alert systems" ahead of Real Madrid vs Manchester City and Atletico Madrid vs Borussia Dortmund in the capital on Tuesday and Wednesday, respectively.
The Santiago Bernabeu holds more than 80,000 spectators, while Atletico's Metropolitano has a capacity of 70,460.
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More than 1,270 security guards are set to be deployed in Madrid as part of heightened security responses to the ISIS threat, La Vanguardia report.
Head of The Ministry of the Interior, Fernando Grand-Marlaska, said: “In terms of preventing the terrorist threat, the State Security Forces and Bodies have activated all their early warning and protection systems, as well as all their response mechanisms ready and willing.”
He added that all pertinent initiatives have been adopted to guarantee the safety of both the participants and attendees of the sporting event and the Spanish citizenry as a whole, local media report.
That includes more than 2,000 agents from the National Police and the Civil Guard, who will be joined by members of the Municipal Police.
The response from Spanish authorities has been conducted in line with the Anti-Terrorism Prevention, Protection and Response Plan for the current level 4 out of 5 anti-terrorist alert.
Also taking place tonight is Arsenal's highly-anticipated clash with Bayern Munich in the capital.
The Met Police said it has a 'robust policing plan' in place for the game at the 60,704-capacity Emirates Stadium on Tuesday.
Deputy Assistant Commissioner Ade Adelekan, overseeing the policing of London today, said: "The UK terrorism threat level remains at ‘substantial’ meaning an attack is likely.
"We work closely with colleagues from across Counter Terrorism Policing in planning for events here in London, to take into account any relevant information that could help us to keep those attending safe.
"We're aware of online and media reports in relation to calls to target matches across Europe and here in London.
"However, I want to reassure the public that we have a robust policing plan in place for tonight's match and we continue to work closely alongside the club’s security team to ensure that the match passes peacefully.
“As ever, we ask the public to remain vigilant, and if they see any that doesn’t look or feel right, then report it to police or security staff.”
Security will also be stepped up for PSG's clash with Barcelona in Paris on Wednesday.
A French Interior Ministry source told The Sun: "Security will be enforced to counter any threats.
"Specialist anti-terrorist teams will be in place, along with soldiers outside the ground."
There will be some 500 ordinary police alone securing the game, and these will be swelled by an unspecified number of specialist units, including military ones.
PSG has also reported cyber attacks on its ticketing system over the past two days.
This raises the fear that terrorist are attempting to gain access to the stadium, said the Interior Ministry source.
France has already increased its security alert rating to the highest level after ISIS claimed responsibility for the deadly attack on Crocus City Hall in Moscow last month.
It resembled the November 2015 attacks on Paris, when ISIS operatives struck across the city, killing 130 people, and wounding hundreds of others.
The night of violence started with an attack on the Stade de France, when suicide bombers hit an international match between France and Germany.
England fans have already been warned over new terrorism threats ahead of this summer's Euro 2024 in Germany.
German Interior Minister Nancy Faeser said the Islamist attack in Moscow has raised “dangers to a new level”, with drastic steps being taken already.
That includes a plan to temporarily close borders and ramp up frontier checks, while British police will also make the journey to help bolster ranks in the host country.
