Vietnam on Thursday objected to the United States adding it to a human trafficking blacklist, saying the move was based on "inaccurate information".
On this year's assessment of 188 countries' efforts to combat trafficking, the US State Department downgraded Vietnam -- as well as Cambodia, Brunei and Macau -- to the worst tier, alleging weak efforts to stop forced sex work or help migrant labourers.
A Tier 3 ranking opens countries up to US sanctions, although Washington routinely waives punishment for friendly governments that promise action.
Vietnamese foreign ministry spokeswoman Le Thi Thu Hang said the State Department had based its findings on "inaccurate information", and they "did not fully and accurately reflect the situation and efforts to prevent and combat human trafficking in Vietnam".
"We hope the US will cooperate more closely in the coming time to have a full assessment of Vietnam's efforts to prevent and combat human trafficking," she said in a statement on the ministry website.
US-Vietnamese ties have been warming, not least because of shared concerns about China.
But the State Department said prosecutions of trafficking dropped off in 2021, and especially found fault with Hanoi allowing a Vietnamese diplomat to remain at his post after he and another embassy staffer in Saudi Arabia were accused of directly facilitating forced labour.
