Censor.NET reports citing CNN.
Prosecutors General's Office of Ukraine (PGO) said they have made seven separate appeals over the past two years for help in questioning President Donald Trump's former campaign manager, including letters to FBI Director James Comey and the U.S. Justice Department officials.
Ukrainian officials said the U.S. has not responded to those requests. U.S. authorities confirmed to CNN that the requests were received but declined further comment.
Under a "mutual legal assistance" treaty, the two countries have agreed to regularly assist each other in law enforcement efforts, such as gathering statements and other evidence for prosecutions.
The official requests from PGO in Kyiv started in Dec. 2014, and involve a corruption case targeting Ukraine's former Justice Minister Oleksandr Lavrynovych.
Manafort has not been charged with a crime. Prosecutors want him to testify, Ukraine's prosecutor for special investigations Serhii Horbatiuk said.
Prosecutors allege that Lavrynovych illegally diverted more than $1 million in government funds to a prominent New York City law firm - Skadden, Arps, Slate, Meagher & Flom.