Paul Manafort, the arrested campaign manager for U.S. President Donald Trump, is involved in two investigations being conducted by Ukraine's Prosecutor General's Office (PGO), head of the PGO's department for special investigations Serhiy Horbatiuk has said.

Horbatiuk said money laundering charges involving payments during disgraced ex-President Viktor Yanukovych's tenure are being studied by the PGO.

"The first investigation involves payments by Ukraine's Justice Ministry to an American law firm on the "Tymoshenko versus Ukraine" case and Tymoshenko's unlawful arrest. The second concerns the so-called 'black ledger' [of payments from Yanukovych's Party of Regions to Manafort]," Horbatiuk said during an interview with Hromadske Radio.

According to Horbatiuk, Ukraine's PGO two years ago requested permission from the U.S. Department of Justice to interview Manafort about the payments and how the money was used. Horbatiuk said Ukraine's PGO has still not received an answer from their American colleagues.

Manafort and his colleague Ricky Gates on October 30, 2017 were accused by U.S. Special Prosecutor Robert Meuller 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.