The warning came as exceptionally rainy weather gave way to sunshine and the promise of balmy evenings, when crowds of fans and revellers will be able to watch matches at outdoor venues.
"It's all planned to ensure security at specific places," sports minister Thierry Braillard said
"We cannot accept unorganised crowds because the security forces don't have the means to make them safe," he told RMC radio ahead of the June 10-July 10 tournament.
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Gunmen and suicide bombers killed 130 and injured hundreds more on Nov. 13. Three blew themselves up outside the Stade de France north of Paris, where the Euro contest starts on Friday. Others raked cafe terraces in Paris with gunfire and shot dead 90 people at a rock concert.
The U.S. government warned last week of possible summer attacks in Europe, saying targets could include Euro 2016.
Around 90,000 police, soldiers and private security agents are being deployed to ensure safety for an expected 2.5 million spectators at 51 soccer matches and at official "fan zones" where millions more can watch giant TV screens.
The minister said the government was prohibiting TV screens from public spaces outside the fan zones and that it would be up to city mayors to ensure that cafe terrace events did not spill over into the streets.
(Reporting by Brian Love; Editing by Leigh Thomas and Andrew Roche)
