RIO DE JANEIRO — Ten Brazilians who pledged allegiance to the Islamic State militant group were arrested Thursday, authorities announced, describing them as "amateurs" who discussed on social media the possibility of staging attacks during next month's Olympics.
Justice Minister Alexandre de Moraes said in the capital, Brasilia, that the 10 were being held on two terrorism-related charges and that two more people were being sought.
Authorities said any attack plan would have had little chance of coming to fruition, citing the group's lack of resources and skills.
But officials and security experts argued that police were justified in being aggressive in light of "lone wolf" attacks staged in the U.S. and Europe by men with little or no training.
Moraes said police acted because the group discussed using weapons and guerrilla tactics to potentially launch an attack during the Olympics, which begin in Rio de Janeiro on Aug. 5. They will remain in police custody for at least 30 days.
"They were complete amateurs and ill-prepared" to actually launch an attack, Moraes said. "A few days ago they said they should start practicing martial arts, for example."
He said that there were no specific targets for an attack, but that even disorganized groups have to be taken seriously.
The possibility of an attack is not so "far-fetched" even though Brazil has never been a target for terrorism, said Alex Kassirer, a counterterrorism analyst at Flashpoint, a New York-based intelligence group.
"The Olympics is a really unique opportunity to be able to target a concentration of all of the enemies in one area," she said.
Kassirer pointed out the Islamic State group launched a channel in May on the messaging app Telegram to disseminate jihadi propaganda specifically in Portuguese. On Sunday, another channel vowed allegiance to IS, although its authenticity has not been determined, she said.
The arrests were made in 10 different states, including Sao Paulo and Parana in the southern part of the country, and it was not clear whether the suspects knew each other beyond their online contacts.
Moraes said authorities seized computers, cellphones and other equipment, but no weapons.
Authorities said the investigation that began in April showed the suspects had all been "baptized" as Islamic State sympathizers online but none had actually traveled to Syria or Iraq, the group's stronghold, or received any training. Several were allegedly trying to secure financing from IS.
Investigators said none of the suspects was of Arab descent, but released no details on their religion. They were described as being between the ages of 20 and 40, except for one minor.
Newton de Oliveira, a professor and security specialist at Mackenzie Presbyterian University in Rio de Janeiro, applauded authorities for detecting the group, saying recent world events raised worries about terrorism during the sporting event.
But he cautioned it was hard to say how serious this threat was.
"It's not clear whether we are talking about young people getting carried away or if they were going to move forward with actions," Oliveira said.
The justice minister said one of the suspects communicated with a store in Paraguay via email in an alleged attempt to buy an AK-47 assault rifle, apparently the most concrete action taken toward a possible attack. The email communication was intercepted by police.
Brazilians are allowed to possess small firearms but must have a license and training to do so. Only members of the military may possess assault weapons like the AK-47, although those and other firearms are common in the country, especially in slums controlled by drug gangs.
Last week the top military aide for Brazil's interim government said concerns over terrorism had "reached a higher level" after the truck attack that killed 84 people in Nice, France.
Officials did not raise the country's terror alert level Thursday following the raids.
Security has emerged as the top concern during the Olympics, including violence possibly spilling over from Rio's hundreds of slums. Authorities have said 85,000 police officers and soldiers will be patrolling during the competitions.
This story has been corrected to reflect that the store from which one suspect allegedly tried to acquire an assault rifle is in Paraguay, not Brazil.