The department warned of "arbitrary enforcement of local laws", sudden prohibitions on exiting the country and harassment of U.S. citizens of Chinese heritage. "USA citizens under exit bans have been harassed and threatened", the advisory stated.
The United States warned its citizens Thursday they could face arbitrary action by authorities when they visit China, following the detention of a number of Canadians.
"U.S. citizens may be subjected to prolonged interrogations and extended detention for reasons related to 'state security, '" the advisory says.
"US-Chinese citizens and US citizens of Chinese heritage may be subject to additional scrutiny and harassment, and China may prevent the US Embassy from providing consular services". "Chinese citizens and USA citizens of Chinese heritage may be subject to additional scrutiny and harassment, and China may prevent the US embassy from providing consular services". The three family members, all American citizens, arrived in China in June under USA passports to visit the ailing father of Liu's wife.
China last month detained two Canadians, a former diplomat and a businessman, on charges of activities that 'endanger China's security'.
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The State Department urges travelers to China to keep a US passport with a valid Chinese visa close at hand.
China and Canada both said the case was different to that of Mr Kovrig and Mr Spavor who stand accused of harming national security.
China has detained 13 Canadians since early December when a senior executive of Chinese telecom giant Huawei was arrested in Vancouver on a USA request for alleged violations of Washington's sanctions on Iran, according to Ottawa. Earlier on Thursday, China's top prosecutor said the two Canadians had "without a doubt" violated the law.