ATHENS, Oct 17 (Reuters) - Greek police detained two human rights activists after they unfurled banners at the Athens Acropolis on Sunday opposing the Beijing 2022 Winter Olympics as China"s Games organisers prepare to receive the Olympic flame. The activists staged a brief protest at the Acropolis in the Greek capital early in the morning, holding up a Tibetan flag and a banner reading "Free Hong Kong - Revolution" at a scaffolding surrounding part of the monument. The activists detained were 18-year-old Tibetan student Tsela Zoksang and 22-year-old Joey Siu, a U.S. citizen exiled from Hong Kong. The protest was made hours before a dress rehearsal in Greece"s Olympia, site of the ancient Olympics, of the torch-lighting ceremony for the Games set for Monday. Greek police, with several dozen officers present, were quick to stop the activists. The Chinese capital will become the first city to host both the Winter and Summer Games when it stages the Feb. 4-20 event but, as was the case with the 2008 Beijing Olympics, protests and calls for boycotts over the country"s human rights record have marred the run-up. Rights groups and U.S. lawmakers have called on the International Olympic Committee (IOC) to postpone the Games and relocate the event unless China ends what the United States deems ongoing genocide against Uyghurs and other Muslim minority groups. Chinese authorities have been accused of facilitating forced labour by detaining around a million Uyghurs and other primarily Muslim minorities in camps since 2016. China denies wrongdoing, saying it has set up vocational training centres to combat extremism. Sunday"s dress rehearsal at the ancient stadium of Olympia was hampered by brief spells of rain and heavy clouds, with the torch not being lit by the sun"s rays through a parabolic mirror. Instead, a backup flame from previous rehearsals was used by an actress playing the high priestess. More rain is expected on Monday, with human rights activists pledging more actions until Tuesday"s flame handover to Chinese Games organisers in Athens. The Beijing 2008 Summer Games flame ceremony was also severely disrupted by a string of protests from human rights activists, which was the start of international demonstrations over China"s human rights record leading up to the Olympics.