Durex is the official supplier of condoms at the Games that began July 27, and officials have been closely policing which brands can be promoted at the international event.
But condoms from two other manufacturers — Australian-based Ansell and British-based Pasante — were made available in the Olympic village, Radio Netherlands reported.
A photo posted on Twitter by Australian BMX cyclist Caroline Buchanan showed a bucket of condoms beneath a sign that read: “Kangaroo Condoms: for the Gland Down Under.”
Buchanan joked that the bucket lent credence to rumours that the athletes' village is seeing its share of romantic liaisons.
"Haha, the rumors are true," Buchanan tweeted.
Officials are trying to get to the bottom of who distributed the unauthorized condoms, a spokesperson for the London Olympics organizing committee told the Guardian newspaper.
Ansell and Pasante knew nothing about their condoms being made available to the athletes, Reuters said, quoting spokespeople from the two companies.
Durex has sent about 150,000 free condoms to the athletes' village.