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BEIJING (AP) — Chinese leader Xi Jinping visited the northwestern Xinjiang region this week amid concerns over China’s detention of a million or more members of primarily Muslim ethnic native minorities.

Xi called Xinjiang a “core area and a hub” in China’s program of building ports, railways and power stations connecting it to economies reaching from Central Asia to Eastern Europe, the official Xinhua News Agency reported Thursday.

Under Xi, authorities have carried out a sweeping crackdown on Xinjiang’s native Uygur and Kazakh communities following an outburst of deadly separatist violence.

Critics have described the crackdown that placed thousands in prison-like indoctrination camps as cultural genocide. The U.S. and others have placed officials responsible under visa bans for their part in extra-legal detentions, separation of families and incarcerating people for studying abroad or having foreign contacts.

Xi met with leaders of the Xinjiang Production and Construction Corps, a supra-governmental body that operates its own courts, schools and health system under the military system imposed on the region after the Communist Party’s rise to power in 1949.

Xi “learned about the history of the XPCC in cultivating and guarding the frontier areas,” Xinhua reported.

Xinjiang borders Russia, Afghanistan and volatile Central Asia, which China has sought to draw within its orbit through economic incentives and security alliances.