Paris police prefect Michel Cadot insists his forces are well prepared to deal with any security concerns during Euro 2016.
The terror attacks carried out on Paris in November, killing 130 people, raised fears over the potential for repeat incidents at the European Championship, which gets under way in the capital on Friday.
Earlier on Monday, Ukrainian security agency SBU announced it detained a Frenchman last month who had amassed a cache of guns detonators and large quantities of TNT, with the intention of carrying out mass attacks at the tournament.
Euro 2016 begins when hosts France entertain Romania at the Stade de France, seven months on from the Saint-Denis venue being one of the targets of the co-ordinated terrorist assaults across Paris.
According to French TV network M6, the 25-year-old man identified as Gregory M worked at a farming co-operative in eastern France and had no previous criminal record.
In a media conference on Monday, Cadot stressed the authorities were doing everything in their power to prevent any threat, while over 3,000 people have been added to beef up numbers and provide added security - with more to come.
"Without any doubt, today I believe that these answers give us the means to face this difficult period, during which we'll never be able to say that there's no risk, that the risk is nil," Cadot said.
"It's a difficult period with attacks which could hit our country anywhere, I repeat not only in the fan zones and the stadiums, but yes I think today we're as prepared as we ought to be faced with this challenge.
"If you add them up, although we're not talking down to the last unit, along with the 10,000, with the figures I talked about earlier with a bigger mobilisation of staff from the police prefecture, the Sentinelle military operation, the mobile force...we're talking about well over 3,000 additional people right from the start of the Euros, that means from this week, and this figure will grow from the middle of June."
Despite stringent safety measures at the Coupe de France final between Paris Saint-Germain and Marseille at the Stade de France last month, fans were still able to smuggle in flares, and Cadot knows the security forces must be more vigilant.
"We need to improve," he said. "There will be a close security perimeter and an outer security cordon that will create a bubble even before the checkpoints.
"We are focusing on fan zones and stadiums, but during that period there is a very strong need for the general surveillance of the Paris area."