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.
Updating a travel advisory, the State Department maintained its previous guidance that Americans should "exercise increased caution" in China but stopped short of discouraging visits.
While the language was largely the same as earlier, the State Department warned of "arbitrary enforcement of local laws," sudden prohibitions on exiting the country and harassment of US citizens of Chinese heritage.
"In most cases, US citizens only become aware of the exit ban when they attempt to depart China, and there is no method to find out how long the ban may continue," it said.
"US citizens under exit bans have been harassed and threatened."
It also advised Americans to look out for last-minute security checks and curfews in Xinjiang and Tibet, two minority-dominated regions where Beijing has sought to impose strict control.
Secretary of State Mike Pompeo, asked about the updated advisory in a televised interview, said the State Department wanted Americans to "understand the risk but still travel there when it's appropriate."
"We wanted to let them know that there have been more risks from what China has done in terms of folks traveling there and not being permitted to return," Pompeo told Fox News host Sean Hannity.
China has detained 11 Canadians since early December when a senior executive of Chinese telecom giant Huawei was arrested in Vancouver on a US request for alleged violations of Washington's sanctions on Iran, according to Ottawa.
Two of the arrests -- of former diplomat Michael Kovrig and consultant Michael Spavor -- were widely viewed as retaliation for the arrest of Huawei chief financial officer Meng Wanzhou, who is facing extradition to the United States.
China last year appeared to hit back at the US travel advice by issuing its own guidance to Chinese coming to the United States, warning of the risk of mass shootings and the high cost of health care.
Despite rising political friction, the two countries remain among the top sources of visitors to each other, with China by far the largest provider of foreign students to the United States.