More than 1,000 protesters detained during anti-government riots in Tibet three months ago have not been accounted for, a human rights group said Wednesday. Amnesty International said a quarter of about 4,000 people detained by police during the riots in Tibet in March are unaccounted for. The others have been either released or placed under formal arrest. The Olympic torch will pass through the Tibetan capital, Lhasa, on Saturday, and Amnesty's Asia-Pacific director, Sam Zarifi, said the event should draw attention to the missing and those in prison. "There is very little information coming out of Tibet, but the information we have paints a dire picture of arbitrary detentions and abuse of detainees," he said. "With the torch relay about to enter Tibetan areas, this should be an opportunity to shine some light on the situation there." Buddhist monks in Lhasa held demonstrations against Chinese rule in March. The protests spread across Tibet and turned violent as protesters clashed with police. Chinese authorities responded with a security clampdown and made parts of Tibet off limits to foreign tourists and most of the international media. Amnesty International said police and security forces have confiscated mobile phones and computers from monasteries, nunneries and private homes in Tibet to stop people communicating with the outside world. China says it has ruled Tibet for centuries, although many Tibetans say their homeland was essentially independent for much of that time.