Nearly 10,000 Uighurs involved in deadly riots in China's northwestern Xinjiang region went missing in one night, exiled Uighur activist Rebiya Kadeer said Wednesday, calling for an international investigation.

Kadeer's visit to Tokyo was condemned by China. The vice foreign minister summoned the Japanese ambassador in Beijing to express China "strong dissatisfaction" and to "demand the Japanese government take effective action to stop her anti-China, splittist activities in Japan," the Foreign Ministry said.

In Xinjiang's worst ethnic violence in decades, Uighurs on July 5 attacked Han Chinese in the regional capital of Urumqi after police tried to break up a protest against fatal attacks on Uighur workers at a factory in south China.

Han Chinese in Urumqi launched revenge attacks later that week.

"The nearly 10,000 (Uighur) people who were at the protest, they disappeared from Urumqi in one night," Kadeer told a news conference in Tokyo through an interpreter. "If they are dead, where are their bodies? If they are detained, where are they?"

She called on the international community to send an independent investigative team to Urumqi to uncover details of what had taken place.

The official death toll from the riots stands at 197, most of whom were Han Chinese who form the majority of China's 1.3 billion population. Almost all the others were Uighurs, a Muslim people native to Xinjiang and culturally tied to Central Asia and Turkey.

More than 1,000 people were detained in the immediate aftermath of the riots, and over 200 more in recent days, state media said. None has been publicly charged.

China has accused Kadeer, who lives in exile in Washington, of triggering the riots and of spreading misinformation. It took great glee in pointing out that pictures she said were taken in Urumqi actually came from an unrelated incident in another part of the country.

Kadeer, who rejects the Chinese accusations, said she thought the death toll was much higher after learning that there was random gunfire one night when electricity in the city was shut down.

In a measure of continued nervousness and lack of information in Urumqi, the city government was forced to deny rumors sweeping the Han population that Uighurs were kidnapping Han to exchange them for detained Uighurs, a Chinese newspaper said.

Beijing does not want to lose its grip on Xinjiang. The vast territory borders Russia, Mongolia, Kazakhstan, Kyrgyzstan, Tajikistan, Afghanistan, Pakistan and India, has abundant oil reserves and is China's largest natural gas-producing region.

(Additional reporting by Ben Blanchard and Lucy Hornby in Beijing; Editing by Nick Nacfie)