PlayEight Free Tibet campaigners have been arrested during a protest at which a British journalist was also held.
ITV News reporter John Ray was released soon after the incident at the Chinese Ethnic Culture Park, near the National Stadium.
He was taken away by police as members of the campaign group handcuffed themselves to each other and bicycles
Mr Ray, who has been based in Beijing since 2006, is ITV News' first China correspondent.
ITN, which makes ITV News, said it would be making the "strongest possible" protest.
A spokesman said: "John Ray is a fully accredited China correspondent who was doing his legitimate job as a journalist.
"We intend to protest in the strongest possible terms to the Chinese authorities and seek assurances that the treatment meted out to Mr Ray will not be repeated."
The International Olympic Committee also said it was investigating.
A spokesman said: "The IOC has learned through media reports that a British journalist was allegedly assaulted today while covering a demonstration near an Olympic venue in Beijing.
"The IOC's position is clear: the media must be free to report on the Olympic Games.
"We are endeavouring to discover the full facts of this incident and, if necessary, will raise our concerns with the appropriate authority."
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