After months of denials that contingency plans were being put in place, French President Emmanuel Macron sparked new doubts last month when he said that there was "obviously a plan B, a plan C" for the opening ceremony on July 26.

But Tony Estanguet, who heads the Paris Olympics organising committee, stressed on Wednesday that the location for the ceremony would not change.

"Today, with the artistic director for the ceremony, Thomas Jolly, we are working on an opening ceremony on the Seine. Our teams are not working on any other location," he told France Inter radio.

French security services have consistently raised doubts about having the opening team parade on the river in the heart of the City of Light, citing the difficulty of securing such a large area and the risk of a terror attack or stampede.

With sporting delegations set to sail along the river in a flotilla of around 100 boats, it will be the first time the opening ceremony has taken place outside the athletics stadium in Olympic history.

French Sports Minister Amelie Oudea-Castera called the plans "a key symbol of our ambitions for iconic Games" in an interview earlier this month.

Some media reports have speculated that the ceremony might simply be downgraded in the event of a major terror threat, with the number of spectators limited or just performers, not athletes, permitted to take part.