U.S. Undersecretary of State Wendy Sherman has held talks in Kyiv with Ukranian President Viktor Yanukovych.
The case of the jailed former Ukrainian Prime Minister Yulia Tymoshenko topped discussions on March 20.
Tymoshenko, who led the 2004 Orange Revolution protests that derailed Yanukovych's first bid for the presidency, was jailed for seven years on abuse-of-office charges in 2011.
She is now facing a fresh trial on tax evasion and embezzlement charges.
The Tymoshenko case has soured Ukraine's ties with the West, which saw it as an example of selective justice.
The European Union has delayed the signing of landmark deals on free trade and political association with Kyiv over the issue.
Sherman urged Kyiv to "step back from this very dangerous moment," describing the case against Tymoshenko as "political prosecution.
Based on Reuters and Interfax reporting