"It's completely logical for the armed forces to contribute" to Olympic security, Chief of Defence Staff Thierry Burkhard told defence committee MPs Thursday.

He trailed a deployment of up to 10,000 soldiers -- matching the "Operation Sentinelle" forces created to patrol following 2015's terrorist attacks in Paris.

"Given that it's an exceptional event, there can be an exceptional contribution. The real question for me is planning ahead... given that some things are likely to happen more or less at the last minute," Burkhard added.

Organisers fear private firms will not be able to recruit the over 20,000 civilian staff needed to man Olympic security in time, putting pressure on the army to fill the gaps.

One senior civil servant told AFP that the Games' organising committee "will never manage to recruit the staff they need from private security".

The army "is committed whatever happens, it's just the details of their mission that remain to be decided," said the source, who asked not to be named.

While officers would prefer their troops to carry out only patrol and surveillance missions, "there's a chance the order will come for them to do security checks and filtering," the civil servant said.

Plans currently call for soldiers to protect transport hubs and major routes to the Games, while police cover the approaches to Olympic sites and private security manage access and the space inside the cordon.

Around 2,000 air force personnel will also secure the airspace over Paris, including against drones.

But many expect a repeat of the 2012 London Olympics, when the British government had to deploy 3,000 additional troops days before the competitions started as private security firms fell short.

"If there's only a limited shortfall from private security, we can adapt. If it's huge, that will be a problem... the armed forces will have to fill the gaps," one senior officer told AFP.

Commanders will also have to find accommodation for mobilised soldiers in the Paris region, and are already planning to set up tent cities in case reinforcements are needed.