Military vehicles are now being used to escort all buses heading to an Olympic venue after an attack on one injured two people.
The bus, carrying mostly media representatives, was returning from the Deodoro complex in Rio de Janeiro's northwest to the main press centre on Tuesday when it was hit by stones, smashing two windows, according to Olympic officials.
Some of those on board remain convinced it was hit by gunfire.
Two people suffered minor injuries from flying glass.
The incident came after a bullet tore through the press tent at the equestrian centre at Deodoro on Saturday while another bullet was found not far from the stables at the same venue on Wednesday.
Earlier that day a man was arrested in relation to the press tent incident but only after a gunfight with police.
Police believed the shot had been an attempt to bring down a police blimp or drone, rather than an attack on the Olympic facilities.
Rio communications director Mario Andrada da said security had since been increased at Deodoro and confirmed on Thursday that every bus was now being given a military police escort.
He said security remained the primary concern of Olympic organisers.
"In a sense it is our main mission," Andrada said.
International Olympic Committee spokesman Mark Adams said while security was the responsibility of the Rio organisers, the IOC took all the incidents very seriously.
Andrada said a police report into the attack on the media bus had been completed and was expected to be released on Thursday.