As the Group of 20 summit formally kicked off in Osaka on Friday, Rebiya Kadeer, a prominent political activist for China's Uighur ethnic minority, urged Prime Minister Shinzo Abe to highlight Beijing's alleged persecution of the majority-Muslim group in the country's far west, slamming Japan's inadequate handling of what is shaping up to be one of the top global human rights issues.

"I don't think Japan is playing an adequate role in addressing the issue of concentration camps" in China's Xinjiang region, Kadeer told a news conference in Osaka that coincided with the first day of the G20 gathering of world leaders. Some experts say up to 1.5 million ethnic Uighurs and other Muslims could be held in those facilities, often referred to by Chinese authorities as "re-education" centers.

Although Kadeer lauded Japanese lawmakers, including Abe, for their past establishment of a lawmakers' group seeking to address the human rights issue of Uighurs, she said Tokyo has so far failed to take a firm enough stance with China.