In late 2008, only two weeks after Liu was first held, former president George W. Bush's ambassador to China Clark Randt "urged the Chinese government to release him and stop harassing peaceful dissidents," according to a confidential memo released by WikiLeaks.
Current US ambassador Jon Huntsman later took up the cause in 2009, writing a letter to Foreign Minister Ding Xiaowen to call for Liu's release after he was imprisoned on subversion charges upon co-authoring Charter 08, a bold manifesto calling for democratic reform in one-party, Communist-ruled China.
Ding pushed back, however, calling on Washington to "cease using human rights as an excuse to 'meddle' in China's internal affairs," another cable marked confidential said.
Calls for Liu's release have grown in the last two months after he won the Nobel Peace Prize in a move that sparked fury in Beijing, where officials insist he is a common criminal.
Despite Washington's often soft public approach to Chinese crackdowns on intellectuals and dissidents, the cables point to US diplomats closely following Liu's situation, meeting with his wife and friends, and consistently calling on Beijing to review his case, The New York Times reported.
The memos were part of a cache of a quarter million confidential US diplomatic cables WikiLeaks began making public late last month, in cooperation with a small group of media outlets that includes the Times.