Hillary Clinton’s campaign is questioning Donald Trump’s top political aide’s ties to a pro-Kremlin political party in Ukraine, claiming it is evidence of the Republican nominee’s cozy relationship with Russia.

The New York Times reported that handwritten ledgers found in Ukraine show $12.7 million in undisclosed payments to Paul Manafort, Trump’s campaign manager, from the pro-Russia party founded by the country’s former president Viktor Yanukovych. Investigators are probing whether the money was part of an illegal off-the-book system that may have also made payments to election officials, according to the Times in a story published Sunday night.

“Given the pro-Putin policy stances adopted by Donald Trump and the recent Russian government hacking and disclosure of Democratic Party records,” Clinton campaign manager Robby Mook said in statement, “Donald Trump has a responsibility to disclose campaign chair Paul Manafort’s and all other campaign employees’ and advisers’ ties to Russian or pro-Kremlin entities, including whether any of Trump’s employees or advisers are currently representing and or being paid by them.”

The campaign stepped up criticism Monday by suggesting that Manafort pushed for pro-Russia changes to the Republican Party platform and by suggesting that several Trump advisers have links to Moscow.

Manafort, who has had several international clients including Philippine dictator Ferdinand Marcos, denied any wrongdoing.

“The simplest answer is the truth: I am a campaign professional,” said Manafort in a statement Monday. “I have never received a single ‘off-the-books cash payment’ as falsely reported by The New York Times, nor have I ever done work for the governments of Ukraine or Russia.”

He added that his five-year stint as a political consultant in Ukraine ended after that country’s elections in 2014. A spokeswoman for the Trump campaign did not respond to requests for further comment.

Svitlana Olifira, a spokeswoman for Ukraine’s National Anti-Corruption Bureau, confirmed that documents were recovered, but cautioned that the probe was in early stages.

“It’s a bit early to say if we really will have a separate investigation related to the name of Manafort, since we are still studying it (the documents),” said Olifira. “I want to stress that his name appears there not just once, but we cannot say if he physically received the money assigned to him, as there are other signatures near his name.”

Serhiy Leshchenko, a Ukrainian lawmaker, said he believes that the ledger correctly reflected the funneling of what he called “corrupt money.”

“I’m convinced that this information is accurate and (that these) documents are genuine, because all this content can be confirmed by historical events, evidence and statements by other public figures who are on the list,” Leshchenko said.

Trump’s relationship with Russia has drawn scrutiny throughout the campaign, most recently when he encouraged hackers from that country to find Clinton’s missing emails, an apparent invitation for a foreign power to intervene in a U.S. election. Trump also has frequently praised Russian President Vladimir Putin.

Trump delivered what was billed as a major foreign policy speech on Monday but did not mention the questions surrounding Manafort. He repeated, however, his belief that the U.S. should set aside its differences with Russia to work together to defeat the Islamic State extremist group.

(AP)