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.

During his bilateral meeting with Chinese President Xi Jinping, Abe broached the Uighur rights issue, Deputy Chief Cabinet Secretary Yasutoshi Nishimura said.

Still, Kadeer believes Tokyo can do more.

“I want the Japanese government to realize that whatever China is saying to them about Uighurs is an outright lie, and to dispatch a group of investigators (to Xinjiang) to find out the details of what’s happening,” Kadeer said. She also demanded Japan “raise the issue of Uighurs with the United Nations.”

A former president of the World Uyghur Congress and current president of the Free Indo-Pacific Alliance, a group that represents exiled minorities including Tibetans, Kadeer herself fled China after being labeled a separatist, and now lives in the United States.

China calls the Xinjiang camps “vocational training centers” and says the measures are needed to stem the threat of Islamist extremism. It says thousands of terrorist acts had been orchestrated in the region due to the spread of religious extremism and that authorities have taken a series of measures to prevent such extremism, including the “centers,” which it said has proven to be effective.

China calls the program “preventive” and aimed at educating and rehabilitating individuals influenced by the extremist ideology, with courses on national common languages, legal knowledge and practical skills.

It claims those at the camps have signed agreements that safeguarded all of their basic human rights and that they could go home and receive visits by family whenever they want.

But the story of Uighur Afumetto Retepu appears to belie the official claims by China.

Speaking at a separate news conference on the sidelines of the summit, Retepu, a naturalized citizen of Japan, said an elderly brother-in-law back home in Xinjiang has been missing for nearly two years. It was a year into his disappearance that Retepu learned he had been detained in one of the re-education camps. Retepu says he has no idea when — or if — the brother-in-law will return home.

According to Retepu, while the Japanese government seems to enjoy improved business ties with China, it is ignoring what he believes to be a “genocide” that has befallen Xinjiang.

He further claimed Japan’s Foreign Ministry, without providing a reason why, had initially denied his access to the Osaka summit by refusing to issue a pass that would greenlight his entry — although he was eventually granted one. Retepu said he took this episode as an indication that Tokyo was trying to silence him.

“It’s a sheer disappointment that Japan is not only turning a blind eye to what China is doing but thwarting our attempt to speak out about it,” he said.

When contacted by The Japan Times, a Foreign Ministry official declined to confirm or deny his account of the initial rejection.

Retepu said he doesn’t want to see Japan and China — with their recently improving ties — fall out over the ongoing controversy surrounding Xinjiang. That doesn’t mean, however, that Japan should remain a bystander forever, he said.

“I don’t think Japan should behave in a way that would send out a message to the international community that it doesn’t mind China detaining millions of people indefinitely or killing them as long as its business relations with China remain good,” he said.

U.N. High Commissioner for Human Rights Michelle Bachelet has repeatedly pushed China — unsuccessfully — to allow officials from her branch of the global body access to investigate reports of disappearances and arbitrary detentions in the region.

In March, the U.N. Human Rights Council adopted the outcomes of the Universal Periodic Review — a move that recommended an end to the arbitrary detentions.

At that meeting, Chinese Vice Minister of Foreign Affairs Le Yucheng said the reference to “arbitrary detention” constituted “interference into China’s internal affairs.”

China continues to maintain this stance on the issue while also making independent reporting in the region extremely challenging, with journalists almost constantly followed by plainclothes officials, making it difficult to talk to locals without putting them at risk.

Staff writer Jesse Johnson contributed to this report.