Paul Manafort. Chip Somodevilla/Getty Images

Robert Mueller, the special counsel in charge of the FBI's investigation into whether President Donald Trump's campaign colluded with Moscow during the 2016 election, is collaborating with New York's attorney general while investigating the former Trump campaign chairman, Paul Manafort, Politico reported on Wednesday.

The investigation is reportedly homing in on Manafort's financial transactions, with a particular focus on potential money laundering, and Mueller's teaming up with Attorney General Eric Schneiderman may be a sign the investigation is heating up.

Schneiderman's and Mueller's teams have been sharing evidence and have also spoken frequently about a potential case, sources familiar with the process told Politico. One person added that Mueller and Schneiderman had obtained evidence of possible financial crimes, including money laundering.

Manafort has drawn increased scrutiny from the FBI in recent months. The Washington Post reported that the bureau conducted a predawn raid on his home in July, and agents working with Mueller left Manafort's home "with various records."

Manafort has said he's cooperating with investigators, but the search warrant obtained by the FBI in July suggests that Mueller managed to convince a federal judge that Manafort would try to conceal or destroy documents subpoenaed by a grand jury.

The investigation into Manafort focuses primarily on his work for Party of Regions, a pro-Russia Ukrainian political party.

Manafort is linked to the party through his time serving as a top adviser to Ukrainian President Viktor Yanukovych, a pro-Russian strongman whom Manafort is widely credited with helping win the presidency in 2010. The New York Times discovered last August that the Party of Regions in Ukraine had also designated Manafort $12.7 million in undisclosed cash payments.

Yanukovych was ousted in 2014 after widespread demonstrations against his decision to back out of a deal with the European Union that would have distanced Ukraine from Russia and strengthened ties with the West. Yanukovych fled to Russia amid the protests, during which Ukrainian police officers opened fire on thousands of demonstrators. He is now living under the protection of the Kremlin.

Ukrainian prosecutors have said Yanukovych ordered the security forces' attack on protesters, and at least one human-rights lawyer representing the victims is investigating what role, if any, Manafort played in encouraging Yanukovych's crackdown.

Manafort has additionally been associated with at least 15 bank accounts and 10 companies in Cyprus, dating back to 2007, NBC reported in March, and he was reportedly $17 million in debt to pro-Russian interests by the time he joined the Trump campaign.

As part of his investigation, Mueller also reportedly issued subpoenas to several Washington lobbying firms that have been associated with Manafort's consulting group.

One of those subpoenas was issued to Mercury Public Affairs, and the firm was asked about public-relations work it had conducted for the European Centre for a Modern Ukraine at Manafort's request. The organization's stated goal is to foster closer ties between Ukraine and the European Union as well as the US. It was founded, however, by Leonid Kozhara, a senior member of parliament for the Party of Regions.

Legal experts have said Mueller may be zeroing in on Manafort with the hope that he will become a cooperating witness and perhaps turn on Trump. His collaboration with New York's attorney general could also be part of a broader effort to prompt Manafort's cooperation, because Trump does not have the power to pardon those convicted of state crimes.

Politico reported that a decision had not yet been made on where or whether to file charges. "Nothing is imminent," a source familiar with the case told Politico.

A spokesman for Manafort did not respond to a request for comment.