Mr Macron said it could be "limited to the Trocadéro", across the Seine from the Eiffel Tower, instead of covering the planned stretch of the river.

He added that it could even be moved to the Stade de France, reverting to a traditional ceremony.

The opening ceremony is set to be the first to be held outside a stadium.

More than 10,000 athletes are expected to sail along a 6km stretch of the Seine on some 160 barges.

The organisers had originally planned to accommodate some 600,000 people to watch the ceremony from riverbanks, but that has now been scaled down to 300,000 people.

It has already been revealed that tourists will not be given free access to watch the ceremony, as was originally planned. Instead, tickets will be by invitation only, not via open registration.

"This opening ceremony... is a world first. We can do it and we are going to do it," Mr Macron said in an interview with French media outlets BFMTV and RMC.

But for the first time, he admitted that there were back-up plans in place.

"There are plan Bs and plan Cs", he said, adding: "We are preparing them in parallel, we will analyse this in real time."

Security concerns have been heightened following the threats by the Islamic State group (IS) to Champions League quarter-final football matches in Paris, Madrid and London.

Last week, a post was shared by Al-Azaim Foundation, a media channel responsible for spreading messages from the IS-K branch of the Islamist militant group.

IS-K also claimed responsibility for the deadly attack on Crocus City Hall in Moscow last month.

There are also concerns that the wars in Ukraine and Gaza could increase the security threat, with French authorities mentioning the possibility of a drone attack.

In the same interview, Mr Macron also said he would do "everything possible" to agree an Olympic truce.

The French president was alluding to a historic tradition that peace must prevail during the Olympic Games.

"We want to work towards an Olympic truce and I think it is an occasion for me to engage with a lot of our partners," he said, adding that he had asked the Chinese President Xi Jinping to help him achieve it.

The competition is set to run from 26 July until 11 August. The Paralympic Games then follows from 28 August to 8 September.