Brazil's Justice Minister Alexandre de Moraes attends a press conference on arrests made in at least two states before the start of the Rio 2016 Olympic Games, in Brasilia July 21, 2016. [Photo/Agencies]

RIO DE JANEIRO -- Brazil's federal police have arrested 10 people for allegedly planning terrorist attacks during next month's Olympic Games in Rio de Janeiro.

Justice Minister Alexandre Moraes described the group as "absolute amateurs", adding that their detention was a preventative measure.

Officials said the suspects had tried to make contact with Islamic State, but were not members of the organization.

The arrested people were all Brazilian citizens and were detained in 10 different states. They had been in contact via mobile messaging services like WhatsApp and Telegram, police said.

Thursday's developments came a week after 84 people were killed, including scores of children, when a truck ploughed through a crowd celebrating Bastille Day in the southern French city of Nice.

Brazil's institutional security minister, Sergio Etchegoyen, said after the Nice attack that security would be raised to "another level" for the August 5-21 Games.

Brazil's federal police are understood to be monitoring 100 people for possible links to terrorist groups. Meanwhile intelligence agencies are stepping up security and tightening checks in the tri-border region with Argentina and Paraguay.