Federal police are monitoring about 100 people for possible links to terrorist groups, mostly in the porous tri-border region with Paraguay and Argentina, a presidential aide said on Thursday, requesting anonymity to speak freely.

Brazilian police and intelligence services have been cooperating with French, German, British, Israeli and US intelligence agencies regarding the arrests, the aide said.

“Those involved participated in an online group denominated ‘the defenders of Sharia’ and were planning to acquire weapons to commit crimes in Brazil and even overseas,” Moraes told a news conference.

“It was an absolutely amateur cell, with no preparation at all, a disorganised cell,” the minister said, adding that authorities decided to intervene when the group started to plan actions.

Although Brazil has no history of conflict with known militant groups, Moraes said the Games had made the Latin American country a more likely target, particularly because of participation by countries fighting IS.

“Today was the first operation against a supposed terrorist cell in Brazil,” Moraes said. “Brazil was not part of the coalition against IS, but because of the upcoming Olympics and because it will receive many foreigners, Brazil becomes part of the target.”

The local Olympic organising committee, Rio 2016, referred requests for comment to the federal government.

Brazil has planned an extensive security detail during the Olympics. It will deploy about 85,000 soldiers, police and other security personnel, more than twice as many in place for the London Olympics in 2012.

Brazil is also coordinating closely with partner countries and will operate a joint security centre where representatives from more than 100 countries are expected to help share intelligence and monitor the event.

Moraes said the individuals detained on Thursday were being monitored because they had accessed websites linked to IS.

The group did not have direct contact with IS, though some members had made “pro forma” declarations of allegiance to the militant Islamist group via social media, the minister said. He did not elaborate.

“Those involved participated in an online group denominated ‘the defenders of Sharia’ and were planning to acquire weapons to commit crimes in Brazil and even overseas,” Moraes told a news conference.

The group had “no preparation at all” and was a “disorganised cell,” he said, adding that authorities decided to intervene when the group started planning actions including martial-arts training and the purchase of firearms.

He said a member of the group had contacted a clandestine weapons site in neighbouring Paraguay that sells AK-47 assault rifles, but there was no evidence they acquired any weapons. Two people will be brought in for questioning, in addition to the 10 already detained, he added.

Interim President Michel Temer had called an emergency cabinet meeting following the arrests, the first under Brazil’s tough new anti-terrorism law approved this year.

The minister said the leader of the group was based in the southern Brazilian city of Curitiba, with others spread in nine Brazilian states.

A court in the state of Parana, where Curitiba is based, said there were indications that the group was planning to use weapons and guerilla tactics to achieve its aim.

Brazil’s intelligence agency said on Tuesday it was investigating all threats to the Rio Olympics.

The SITE Intelligence Group that monitors the internet reported the previously unknown group calling itself “Ansar al-Khilafah Brazil” said on the Telegram messaging app on Sunday that it followed IS leader Abu Bakr al-Baghdadi, and had promoted IS propaganda in Arabic, English and Portuguese.

Brazilian authorities stepped up security measures following the truck massacre in Nice, France last week, planning security cordons, additional roadblocks and the frisking of visitors in Rio de Janeiro for the Olympics.