French troops are out in force around Paris's river Seine, equipped with everything from drones to dogs, as the countdown to the riverside Olympic Games opening ceremony ticks towards zero.

Soldiers have "tried to plan for every eventuality" in the four-by-two-kilometre (2.5 by 1.2 miles) zone where 10,000 athletes will stage a waterborne parade on July 26, a senior officer told reporters.

He gave only his first name, Olivier, under French army rules for speaking to the press.

The 800-strong deployment has to contend with a dense urban environment where threats could appear by water or from the air.

And last weekend's narrowly failed assassination attempt on US presidential candidate Donald Trump recalls that any major event is subject to risk of attack.

"It's a complex and unprecedented mission", the officer said, vowing that troops will "adapt to any changes and any evolution of the threat."