One of China's most popular online communities for Muslims has been shut down after posting a petition asking Chinese President Xi Jinping to stop his "brutal suppression" of activists.

The students who wrote the petition told AFP news agency on Wednesday they demanded in the open letter the immediate release of the activists still held by the state.

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"You are not responsible for all of the crimes of the totalitarian system, but as the totalitarian system's head and its commander-in-chief of repression, you must take responsibility for the blood and tears which now flow," the letter said to the president, who came to power in 2012.

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"In the next spring of China's new Jasmine Revolution, who will drive your tanks to crush us, the new generation of students after 1989?"

Yi Sulaiman Gu, a Muslim student studying in the United States at the University of Georgia, said the Zhongmu Wang website - or 2muslim.com - shut the day after he posted the letter to a forum that had previously hosted sensitive discussions on issues such as China's persecution of Muslim dissidents.

"We believed it would be safe for Zhongmu to post it there," Gu said. 

Phone calls to the website's owner went unanswered.

But the letter gained attention when screenshots of it were reposted to China's Twitter-like Weibo website by Xi Wuyi, a professor of Marxism at the Chinese Academy of Social Sciences, who said it proved the site supported separatists in China's restive Xinjiang province.

Violence in Xinjiang - the homeland of China's 10-million strong ethnic Uighur minority - has killed hundreds, with Beijing attributing it to "Islamic extremism" and foreign influence.

"The Chinese government is very unfriendly to the Muslims inside China, especially the Muslims in Xinjiang," said Anthony Chang, a co-author of the letter completing who his bachelor's degree at the University of Queensland in Australia.

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Since 2003, 2muslim.com functioned as an "online network of Muslims sharing Islam", according to archived descriptions.

But as of Wednesday the site was inaccessible, showing only a message stating it was "under maintenance". 

Two of its affiliated social media accounts were also unavailable, displaying messages that declared one account "abnormal" and the other "in violation of required guidelines".

China officially has more than 23 million Muslims, though some independent estimates say there may be as many as 50 million - which would put China among the world's top 10 Muslim nations.

While China's constitution enshrines freedom of religious belief, authorities keep strict limits on it, recognising only five belief systems and seeking to control their messages.

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Source: AFP news agency