Brazilian authorities have arrested 10 people who allegedly pledged allegiance to the militant "Islamic State" (IS) group on social media, reported Brazil's justice minister on Thursday.

The group of mainly Brazilians reportedly discussed buying weapons and using guerrilla tactics to launch an attack during the Olympics, prompting authorities to act, said Justice Minister Alexandre de Moraes.

"There was an order between them to start training in martial arts and to (obtain) ammunition, weapons with which they could carry out an act," the minister told reporters in Brasilia.

"This was in progress. One of them had got in contact with an underground weapons site in Paraguay, asking to buy an AK47" assault rifle.

Federal police are still looking for two additional suspects, de Moraes added. The justice ministry said the operation involved 130 officers and spanned nine states in Brazil.

Interim President Michel Temer called an emergency cabinet meeting in light of the planned terrorist plots, said the presidency.

The group planned to strike during the Olympic Games which begin August 5 in Rio de Janeiro. It was not immediately clear how far the plans had progressed.

"They were complete amateurs and ill-prepared" to actually launch an attack, Moraes said. However, Moraes said even underprepared groups should be taken seriously.

On Tuesday, Brazil's intelligence agency said it was investigating all possible threats to the Rio Games after a previously unknown Brazilian Islamist group pledged their allegiance to IS.

Authorities in Brazil stepped up security measures following the deadly truck attack in Nice, France last week by planning road blocks and frisking of visitors.

(DW)