About 23,000 police, including special forces, will provide security for this year’s Tour de France cycle race.
French Interior Minister Bernard Cazeneuve said exceptional measures would be in place with soldiers guarding key landmarks.
He said the “terrorist threat” following November’s Paris attacks remained “very high”.
France has been in a state of emergency since the jihadist-claimed assaults. The tour runs from 2-14 July.
The emergency was extended last week by the French parliament to cover the Tour and next month’s European football Championship.
Mr Cazeneuve said that the CIGN, an elite police unit, would be on duty throughout the Tour and “ready to intervene at any time if needed”.
He said it was necessary for the security forces to be “extremely vigilant” during the race because they were up against “a determined enemy willing to strike at any moment”.
Correspondents says the event – which covers a route of 3,519km (2,247 miles) and attracts up to 12 million spectators – is notoriously difficult to police because crowds gather informally on innumerable narrow mountain roads and city streets.
The group known as Islamic State carried out last November’s assaults on bars, restaurants, a concert hall and a stadium in which 130 people were killed.
The Tour de France is a multiple stage race that has been held annually – apart from in wartime – since 1903.