Security will be reinforced at Champions League quarter-final matches on Tuesday and Wednesday after a communication outlet supporting the Islamic State group published threats against stadiums.
European football's governing body UEFA said all four games in Paris, Madrid and London would go ahead despite the jihadist threat.
French Interior Minister Gerald Darmanin said security would be "considerably reinforced" when Paris Saint-Germain take on Barcelona in the first leg at the Parc des Princes on Wednesday.
Darmanin said there had been "a clear threat publicly expressed by the Islamic State".
"The police, whom I spoke to very early this morning, have considerably reinforced the security measures," the minister told reporters.
PSG coach Luis Enrique said in his pre-match news conference: "I hope it is a thing we can control and that they are just threats and that nothing will happen."
A French source close to the issue told AFP: "IS has threatened the Champions League quarter-finals, not specifically in France, through one of its communication outlets."
Two games are taking place this week in Madrid -- Real Madrid host Manchester City on Tuesday, while Atletico Madrid face Borussia Dortmund on Wednesday.
Pilar Alegria, speaking for the Spanish government, said more than 2,000 police would be deployed "to guarantee total security".
"We are going to have an exceptional deployment of security services, in line with the level of alert set out by the intelligence services," Francisco Martin Aguirre, the government's delegate for Madrid, said in a video message.
In London, where Arsenal take on Bayern Munich at the Emirates Stadium on Tuesday, the Metropolitan Police said it was aware of the calls to target matches.
"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," Deputy Assistant Commissioner Ade Adelekan said.
UEFA said all the matches would be played.
"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," the statement said.
"All matches are planned to go ahead as scheduled with appropriate security arrangements in place."
The pro-IS channel that published the calls for violent attacks featured images of the Emirates Stadium, the Santiago Bernabeu and Metropolitano stadiums in Madrid, as well as the Parc des Princes in Paris.
Many European countries are on their highest possible terror warning level after Islamic State claimed responsibility for an attack on a concert venue in Moscow last month which killed more than 140 people.
