The World Anti-Doping Agency (WADA) confirmed the leaking of further athlete data by Russian cyber hackers.
Just a day after the first leak by 'Fancy Bear', the information of 25 Olympic athletes from eight countries was released on Wednesday.
WADA said it included 10 from the United States, as well as competitors from Germany (five), Great Britain (five), the Czech Republic, Denmark, Poland, Romania and Russia (all one).
WADA director general Olivier Niggli said: "WADA is very mindful that this criminal attack, which to date has recklessly exposed personal data of 29 athletes, will be very distressing for the athletes that have been targeted; and, cause apprehension for all athletes that were involved in the in the Rio 2016 Olympic Games.
"To those athletes that have been impacted, we regret that criminals have attempted to smear your reputations in this way; and, assure you that we are receiving intelligence and advice from the highest level law enforcement and IT security agencies that we are putting into action.
"Given this intelligence and advice, WADA has no doubt that these ongoing attacks are being carried out in retaliation against the Agency, and the global anti-doping system, because of our independent Pound and McLaren investigations that exposed state-sponsored doping in Russia.
"We condemn this criminal activity and have asked the Russian Government to do everything in their power to make it stop.
"Continued cyber-attacks emanating from Russia seriously undermine the work that is being carried out to rebuild a compliant anti-doping program in Russia."
WADA said its belief was that access was obtained "through spear phishing of email accounts", leading to passwords being stolen.
The Williams sisters, Venus and Serena, and gymnastics superstar Simone Biles - a four-time gold medallist at Rio 2016 - were among the athletes whose information was accessed by the group on Tuesday.
There is no evidence of any wrongdoing by the athletes involved, with the hackers having disclosed instances where therapeutic use exemptions (TUEs) have been granted, enabling competitors to use medications for legitimate reasons.