Federal police in Brazil have ordered the detention of 12 people who allegedly pledged allegiance to the Islamic State group via social media.
Justice Minister Alexandre de Moraes told journalists in Brasilia on Thursday that 10 had been arrested and two more were being sought.
Moraes says police acted because the group had been discussing the use of weapons and guerrilla tactics to potentially launch an attack during the Olympics, which begin Aug. 5.
The suspects are all Brazilian and had never traveled to meet with anyone connected to ISIS, authorities said..
The arrests were made in the southern states of Sao Paulo and Parana. Moraes says there were no specific targets for attack.
Last week, Brazil's interim government's top military aide said the concerns with terrorism had "reached a higher level" after the attacks of six days ago in Nice, France.
Rio expects more than 10,000 athletes and half a million tourists. But the city that is already plagued by violent crime is battling a crime wave ahead of the games, reported CBS News correspondent Ben Tracy.
Human body parts recently washed up on Copacabana Beach next to the Olympic beach volleyball arena. Gunmen stormed a hospital to free a suspected drug trafficker and ended up killing a patient, and some Olympic athletes have been mugged on the street. But during the games, the Brazilian government said 47,000 police officers and 38,000 soldiers will be on patrol in Rio -- twice the size of the security force at the 2012 London Olympics.
Rio's state security secretary said the city's security apparatus - including command centers - was successful during the 2014 World Cup held in Rio and the Pope's visit in 2013. Despite budget cuts, he said there is enough money to secure the games, but the security of the city before and after the Olympics will be worse. That is true in some of the poorest favelas, where the police are not always friendly.