GAMES: Rio de Janeiro's mayor has apologised for the daylight robbery of an Australian Paralympian in the Olympic City, describing it as "unacceptable".

 Rio Mayor Eduardo Paes says security will be vastly improved when the city hosts the Olympics from August 5.

 "We know the security challenges of Rio. I am certain they will be better during the Games," Paes told reporters in Rio.

 Australian Paralympic sailor Liesl Tesch and physiotherapist Sarah Ross were robbed on Sunday, saying they were threatened with guns, pushed to the ground and had their bikes stolen while training in Rio.

 The robbery prompted the Australian Olympic Committee (AOC) to write to Games organisers, demanding they mobilise security forces ahead of scheduled.

 Australia's chef de mission Kitty Chiller questioned the level of security for the Games, saying on Tuesday the planned 100,000-strong security force "doesn't seem ... enough".

 Chiller said the robbery of Tesch and Ross wasn't an isolated incident.

 "There have been several incidents over the last couple of months involving our team members and other Australians in Rio," she said.

 "We are demanding that steps and measures are taken to ensure that all our team members who go to Rio for the Olympic Games next month will be safe."

 Mayor Paes, speaking to reporters in Rio at an economic briefing for the Games, acknowledged "the city of Rio is a city with problems".

 He said it was unfair to compare Rio with other Olympic cities in developed nations.

 "The Olympics were never a panacea for the city of Rio," he said.

AAP