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(CNN) —  

The US Department of State is urging those traveling to China to “exercise increased caution,” warning that US citizens could be prevented from leaving China due to its “coercive” use of exit bans.

In an updated advisory released Thursday, the State Department kept China at Level 2 – the same as 2018 – “due to arbitrary enforcement of local laws as well as special restrictions on dual U.S.-Chinese nationals.” However, it expanded upon the potential risks posed to US citizens by the country’s exit bans.

“Chinese authorities have asserted broad authority to prohibit U.S. citizens from leaving China by using ‘exit bans,’ sometimes keeping U.S. citizens in China for years,” the advisory said.

“China uses exit bans coercively: to compel U.S. citizens to participate in Chinese government investigations, to lure individuals back to China from abroad, and to aid Chinese authorities in resolving civil disputes in favor of Chinese parties,” the advisory warned.

The advisory noted that US citizens under exit bans “have been harassed and threatened,” and that most don’t find out about the exit bans until they attempt to leave the country.

“There is no method to find out how long the ban may continue,” the advisory said.

The State Department warned that citizens “may be detained without access to U.S. consular services or information about their alleged crime.”

“U.S. citizens may be subjected to prolonged interrogations and extended detention for reasons related to ‘state security.’ Security personnel may detain and/or deport U.S. citizens for sending private electronic messages critical of the Chinese government,” the advisory said.

The advisory also warned that China does not recognize dual nationality, and “U.S.-Chinese citizens and U.S. citizens of Chinese heritage may be subject to additional scrutiny and harassment.”

According to a State Department official, “the Department of State routinely updates our Travel Advisories and country-specific information for all countries based on a comprehensive review of all available safety information and ongoing developments.”

“At a minimum, we review Level 1 and 2 Travel Advisories every 12 months. The previous Travel Advisory for China was issued in January 2018; the new Advisory was updated as part of the regular annual review and reaffirms China at a Level 2,” the official said.

In a recent high-profile case, Victor and Cynthia Liu, and their mother, Sandra Han, are believed to have been prevented from leaving China. where they have been held since June. All three are US citizens.

US authorities told CNN they are working closely with the two Liu children, who are reportedly being used to pressure their father, Liu Changming, a high-profile Chinese fugitive, into returning to Beijing, where he is wanted for financial crimes. China has accused the Liu family of being “involved in economic crimes.”

US national security adviser John Bolton said in a Twitter post in November that “these Americans need to be allowed to return home.”

CNN’s Ben Westcott and Sarah Faidell contributed to this report.