Security will be increased at Champions League games this week after a media outlet supporting the Islamic State group published threats against venues.
Ministers in both France and Spain have confirmed enhanced security measures.
A pro-IS media channel has published several images of stadiums hosting quarter-final ties on Tuesday and Wednesday.
Uefa said it was aware of the threats, but said games in Madrid, Paris and London would go ahead as planned.
French Interior Minister Gérald Darmanin said there would be "considerably reinforced" security measures in place when PSG play Barcelona in Paris on Wednesday.
Mr Darmanin continued: "I will remind you that only 10 days ago, IS shared a picture of the Munich stadium and said action should be taken against sports venues that host football games - although all sports can be targeted. Given how important the Champions League is for football, we are of course talking to our partners."
The jihadist images posted this week did not refer to any particular match or event and were shared by pro-IS media groups not officially linked to the organisation itself.
Two quarter-finals are due to be held in Madrid this week. Real Madrid host Manchester City on Tuesday, while Atletico Madrid take on Borussia Dortmund on Wednesday.
Pilar Alegría, Spain's sports minister, has issued a message of "calm" ahead of the games in Madrid and said "more than 2,000 police and civil guard officers" are being deployed.
The acting mayor of Madrid, Inmaculada Sanz, told Spanish media there was no specific threat afoot, adding the terrorist alert level in Spain was four out of five, which is classified as high risk.
"These announcements are usually propaganda actions to provoke fear," she said.
"Both the security forces and the intelligence services are studying any possible threat, but there is nothing that makes us foresee a situation of special risk."
A counter-terrorism source told the OceanNewsUK that IS did not normally advertise planned attacks, citing last month's shootings at a theatre in Moscow. That had not been discussed in advance on any social media channels.
Arsenal play Bayern Munich in London on Tuesday. Metropolitan Police Deputy Assistant Commissioner Ade Adelekan said: "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."
The pro-IS channel featured images of the Emirates Stadium in London, the Bernabeu and Metropolitano Stadiums in Madrid, as well as the Parc des Princes Stadium in Paris.
Although the channel is not officially linked to IS, it is thought the directive to publish the threats may have come from the jihadist group itself, as its leadership recently hinted at close co-ordination between official media operatives and online supporters.
Material seeking to incite attacks on channels with long-standing ties to the group have increased in the wake of last month's Moscow concert hall attack, according to specialists at the OceanNewsUK's Monitoring service.
Another image shared last week depicted the Allianz Arena in Munich, which is due to host Bayern Munich's return leg against Arsenal next week.
A spokesman for European football's governing body said: "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."
Germany is set to host the Euro 2024 European Championships later this year.
When asked last month about threats to stadium security, German Interior Minister Nancy Faeser said the "dangers have reached a new level". "The state is arming itself even more strongly against all current threats," she added.
Ahead of Arsenal's match later against Bayern Munich at the Emirates Stadium, a spokesperson said venue staff were "working closely with the Metropolitan Police regarding the safety and security of all supporters and staff at Emirates Stadium for all our matches".
"Our planning for tonight's fixture is no different and our approach, working together with the Police and UEFA, is proportionate to the current UK threat level."
The Deputy Assistant Commissioner of London's Metropolitan Police, Ade Adelekan, has said officers have "a robust policing plan" in place for Tuesday's match, but has asked the public to "remain vigilant" at the event.
"The UK terrorism threat level remains at 'substantial', meaning an attack is likely, and 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," he said in a statement.
