France is stepping up security for Euro 2016 with an additional 1,200 military personnel deployed in the greater Paris area, officials said Monday.
The measures were agreed at meeting of the defence and interior ministries, Paris police prefect Michel Cadot said.
The increased security came as Ukraine said it detained a Frenchman suspected of planning a series of terrorist attacks across France during Euro 2016.
Ukraine Security Service chief Vasyl Hrytsak said Ukraine "managed to prevent 15 terrorist acts planned to be carried out on the eve of and during the European football championship in France," according to state news agency Ukrinform.
Cadot said the danger of a terrorist attack during the tournament, which kicks off on Friday, was still high although authorities had no concrete indications of a threat.
France has extended its state of emergency, introduced after the terror attacks in Paris last November, until the end of July.
Security is being heightened around the venues in Paris and Saint-Denis near Paris, fan zones and public areas including transport, tourist and business areas.
Around 13,000 security personnel will be deployed in the Paris area, and around 90,000 across the country.
In a radio interview on Sunday, President Francois Hollande said: "We have invested all the means to succeed, and we must not allow ourselves to be pressured by the threat." But warned: "It exists, this threat."
Euro 2016 begins on Friday when hosts France play Romania in the opening match at the Stade de France in Saint-Denis.
Fifty-one matches will be played at 10 venues, with the final at the Stade de France on July 10.