"We will continue to stand with our partners and allies to promote greater respect for human rights and fundamental freedoms in China," the US Department of Foreign Affairs said in a statement on Thursday.
Gui Minhai was sentenced on February 24 to ten years in prison. He was arrested in 2015 and has been in custody ever since. China accuses him of providing foreign power with intelligence.
China also claims that the Swedish publisher in 2018 applied for Chinese citizenship, and that he thereby terminated his Swedish because China does not recognize dual citizenship.
Earlier, the European Commission has also expressed its support for the imprisoned publisher.