The organising committee of Euro 2016 has received no formal warnings of terror threats to the tournament but is promising unprecedented levels of security to protect fans in France.
Jacques Lambert, the president of Euro 2016 SAS, said the organisers, 10 host cities and French government were united in their belief that France can and will stage a safe and successful event.
Both he and his director general Martin Kallen urged fans to get to the grounds early, as there will be double security checks, and they reassured visitors that the 10 fan zones will be the best places to watch games on big screens.
Lambert, Kallen and UEFA's acting general secretary Theodore Theodoridis were speaking to the media at the Stade de France, where the tournament starts on Friday evening with the hosts playing Romania.
But they were speaking one day after the Foreign Office warned travelling British fans that any site linked to Euro 2016 was a potential target for terrorists.
"My message is clear: we have no knowledge of targeted, concrete threats within a stadium or other venue at Euro 2016," said Lambert.
"I believe the messages that have come from a number of countries are understandably precautionary but we are in constant touch with the French security services and they are contact with their partners in Europe and elsewhere."
Security at the tournament, which runs until July 10, has been the dominant issue in France since last year's terror attacks in Paris and the recent bombings in Brussels.
The tension was ratcheted up this week when Ukrainian officials revealed they had arrested a French national trying to smuggle an arsenal of weapons back to France in order to attack 15 different sites during Euro 2016.
"We've worked hand in hand with the relevant authorities for the last four years to bring the best possible event to the fans," said Lambert.
"Everybody is up to speed and nobody is unaware of what has happened in France or Europe in regards to security.
"We've had to deal with what was imposed upon us but we have wanted to stay focused on delivering the best possible Euros, regardless of external circumstances that we couldn't control.
"Yes, we've had to stiffen our security measures, and we've worked with the French government to find the most effective measures possible.
"But our eternal goal these last few months has been to move out of this negative spiral that we've found ourselves in."
Those stiffened measures at the stadia and fan zones will be two perimeters of security, the first coming before you get to the stadium gates, which may include X-ray machines for certain entrances and games.
Every stadium will be open three hours before kick-off and fans are encouraged to come early, particularly as there will be entertainment laid on at the venues, including the broadcast of earlier games on big screens if applicable.
"What is important is that fans come early - don't leave it until the last moment," said Kallen.