Ukraine's Prosecutor General's Office (PGO) is preparing new requests to the United States for interviewing American political advisor Paul Manafort, who was a consultant to disgraced ex-Ukrainian President Viktor Yanukovych and whose surname appears in the so-called "black books" of Yanukovych's Party of Regions, Radio Free Liberty/Radio Europe said on Thursday.

"Yes, of course, we are preparing requests for assistance, for documents," head of the PGO's special investigations department Serhiy Horbatiuk told RFE/RL. He added that charges in the U.S. against Manafort for laundering money overlap with PGO investigations are underway.

According to Horbatiuk, Ukraine sent the U.S. Justice Department and the U.S. Federal Bureau of Investigations requests for assistance in December 2014. They pertained to ex-Ukrainian Justice Minister Oleksandr Lavrynovych's, his assistant's and then head bookkeeper's dealings with the U.S. Skadden law firm, which was retained by Ukraine during 2011 for $1 million to investigate decisions taken by ex-Ukrainian Prime Minister Yulia Tymoshenko.

"We asked for permission then to question employees of Paul Manafort's firm," Horbatiuk said.

Manafort and his colleague Ricky Gates on October 30, 2017 were accused by U.S. Special Prosecutor Robert Mueller of money laundering, tax evasion and other charges. The "conspiracy against the U.S." was allegedly carried out with the cooperation of Yanukovych and his Party of Regions.

Manafort and Gates became the first persons charged in Mueller's investigation of possible cooperation between Trump's election campaign and Russia during 2016. Both men surrendered to the U.S. Federal Bureau of Investigation. Manafort and Gates are accused of laundering more than $18 million through offshore accounts.