"Many [threats] are discarded and the ones that deserve attention are investigated exhaustively," the agency said.
Earlier this week, a jihadi channel on the messaging app Telegram called for attacks against the Games and detailed targets and methods, according to the SITE Intelligence Group.
SITE said a message was posted to "Inspire the Believers!" saying, "Lone wolf from anywhere in the world can move to Brazil now." The message also suggested using the Games to target the enemies of jihad, including Western athletes, and said it would introduce the hashtag "#RioLW."
Security experts said Brazil has no history of jihadi activity and no established terror networks, making it difficult to pull off a complex attack at the Olympics. However, like many other cities, Rio faces the threat of an individual, or "lone wolf," terrorist and those are the people jihadi social media are hoping to reach.
"There is a concern, it has to be taken very seriously, but I also have a lot of faith that the Brazilian authorities are doing everything they can and we have to give them credit," said Sajjan Gohel, international security director at the Asia Pacific Foundation.
Tightening security after Nice
In the aftermath of the attack in Nice, France, Brazilian authorities said they were reviewing their Olympic security plan, widening perimeters around venues and adding checkpoints and traffic restrictions.
About 85,000 police, soldiers and firefighters will be on duty for the Games, more than double the number in London four years ago. On Wednesday, more than two weeks before the opening ceremonies, troops appeared on popular beaches, including Copacabana.
The Brazilian government confirmed to CNN that four people were rejected for Olympic accreditation because of suspected links to terrorism, out of 500,000 original applications.
Enrico Canali, spokesperson for Brazil's secretary of special events, a branch of the Justice Ministry, said a search of international databases revealed these four were wanted by police. He declined to identify their nationalities.
A Brazil chapter of ISIS?
On July 17, a group calling itself Ansar al-Khilafah Brazil, appeared on Telegram pledging its allegiance to ISIS leader Abu Bakr al-Baghdadi and posting ISIS propaganda in Portuguese, according to SITE.
Earlier in the month, Andrei Rodrigues, security chief for the Olympic Games, said while Brazil was preparing for the worst-case scenario, he was not surprised ISIS was turning to Portuguese-language propaganda ahead of the Games.
"There's nothing new here. It's a well-known fact that they use information and media to promote their ideas and recruitment," he said to CNN in an interview earlier this month.
There are many doubts about the authenticity of those claiming to represent a Brazilian branch of ISIS, including by some jihadists. Intelligence firm Flashpoint had "not seen any credible evidence substantiating such reports."
Flashpoint's analysis describes skepticism from jihadists posting on an ISS-affiliated website, including one reading "this is strange news as we have never heard of jihadi movements in this region."
Gohel said he believes posts about a Brazilian branch of ISIS are concerning but he's confident Brazil is taking it seriously.
"Their telegram channel is not just producing messages in Arabic or English but also Portuguese, which is the indigenous language to Brazil. But the authorities are monitoring it, " he said.
Brazilian officials said they are sharing information not just among themselves but with foreign governments. They've even set up an international counterterrorism center, the first of its kind at an Olympics Games, to try to stop whatever threats await Rio 2016.