Brazil's authorities are seeking to reassure the world that they are prepared to deal with any security issues at this year's Olympic Games in Rio de Janeiro, including an unlikely terrorism threat.

"We always worked with this possibility," Rio's state security secretary José Mariano Beltrame told a press conference on Thursday. "Terror is the number one priority."

Beltrame said this was also the case during last year's World Cup and the 2013 papal visit, which both passed without major incident.

"We receive, or have access to bulletins from ABIN [Brazil's intelligence agency] of possible threats, which haven't yet changed," Beltrame said, referring to heightened worries about vulnerability to terrorism in the wake of the attacks in Paris last week. If notification did arrive, he said, "we have a contingency force."

This week the Brazilian army also launched a special operation called Operation Dynamo to inspect companies that are registered to legally hold explosives in an effort to ensure these do not find their way into the hands of potential aggressors ahead of the Olympics.

Meanwhile, the federal government official responsible for the security of major events, Andrei Rodrigues, has said security preparations for the Olympics would continue as planned with the deployment of 85,000 officers during the Games, around double the number used in London.

Brazil has no history of acts of terror and is not engaged in conflicts in the Middle East, making the country itself an unlikely target, but some experts question whether Rio is genuinely prepared to detect or manage a terrorism threat should one arise.

"There's a tendency in Brazil to equate improving security with increasing security personnel," said Lloyd Belton, a political and country risk analyst at the consultancy firm S-RM.

"Quality often trumps quantity and you can't have an effective counter-terrorism strategy without a well-funded and dynamic intelligence agency," he added. "The country's intelligence agency is chronically underfunded."

Mr Belton said the budget for the intelligence agency was just US$206 million compared with the US$1.27 billion budget for the Ministry of Sport.

But while some worry about preparedness in the event of a threat, social activists are concerned that the excuse of terrorism could lead to a clamp down on legitimate protests.

The Congress is currently debating an anti-terrorism law that the government says is necessary to bring Brazil in line with international anti-terror standards. But opponents fear it could be used to criminalize demonstrations that contain even the slightest hint of violence.

Meanwhile, French police, including some who were in the Stade de France during the attacks in Paris, are training officers in Rio in crowd control.

"We were thinking about not coming but this exchange had been planned for some time," chief corporal Antonio José Marçalo told reporters.

The members of the French national police, the CRS, are due to spend two weeks training members of Rio's Choque battalion, a special unit normally used for crowd control and civil disturbances. Officers said the training may include how to deal with terror threats or attacks.

At a display put on for foreign correspondents to show how the Choque is preparing for the Olympics this week, French officers looked on as the Brazilian squad used smoke grenades and sound bombs to simulated a civil disturbance and demonstrated techniques for arresting assailants (pictured above).

"The French police have experience from the World Cup in 1998 and various protests, and they can share this with us," unit commander Henrique Silva said. "The geography of Paris is very similar to Rio, with big avenues for crowd dispersal."