Some International Olympic Committee officials cut a deal to let China block sensitive websites despite promises of unrestricted access, a senior IOC official admitted on Wednesday.
Persistent pollution fears and China's concerns about security in Tibet also remained problems for organisers nine days before the Games begin.
China had committed to providing media with the same freedom to report on the Games as they enjoyed at previous Olympics, but journalists have this week complained of finding access to sites deemed sensitive to its communist leadership blocked.
"I regret that it now appears BOCOG has announced that there will be limitations on website access during Games time," IOC press chief Kevan Gosper said, referring to Beijing's Olympic organisers.
"I also now understand that some IOC officials negotiated with the Chinese that some sensitive sites would be blocked on the basis they were not considered Games related," he said.
Attempts at the main press centre to access the website of Amnesty International, which released a report on Monday slamming China for failing to honour its Olympic human rights pledges, continued to prove fruitless by mid-week.
Other websites, including those relating to the banned spiritual group Falun Gong, are also inaccessible.
Beijing organisers said censorship would not stop journalists doing their jobs in reporting the Games.
"We are going to do our best to facilitate the foreign media to do their reporting work through the Internet," BOCOG spokesman Sun Weide told a news conference.
"I would remind you that Falun Gong is an evil, fake religion which has been banned by the Chinese government."
Reporters without Borders, a Paris-based media watchdog, said it was increasingly concerned that there would be many cases of censorship during the Olympics.
