WASHINGTON -- The special counsel is now looking into the Trump business empire as part of its investigation of Russian meddling in the 2016 presidential election, and whether anyone in the Trump campaign was involved.

In a wide-ranging interview with The New York Times, President Trump had a warning for special counsel Robert Mueller: Investigating his finances and his family's finances would cross a red line.

"I think that's a violation," Mr. Trump said. "This is about Russia."

But investigators are already examining the financial dealings of Mr. Trump and his associates, not limiting themselves to possible collusion with Russia in the 2016 election. Mr. Trump's business ties to Russians go back decades.

The special counsel's mandate is broad and allows him to investigate "any matters that arose or may arise directly from the investigation."

"Speaking for myself, I own nothing in Russia. I have no loans in Russia. I don't have any deals in Russia," Mr. Trump said in a February press conference.

CBS News has confirmed Mueller is also looking into the business dealings of former Trump campaign chairman Paul Manafort, an investigation initiated by federal prosecutors in the Southern District of New York.

The head of the public corruption unit at the Southern District, Andrew Goldstein, recently joined Mueller's team. He oversaw the Manafort probe.

Prosecutor Andrew Weissmann, an expert in financial fraud, is another member of Mueller's team. Weissmann helped lead the federal task force that investigated corruption at energy giant Enron.

With multiple and overlapping probes from the Department of Justice to Capitol Hill, some investigators are also looking into purchases of units in Trump properties.

The Senate Intelligence Committee is poring through thousands of pages of financial records from a unit in the Treasury Department that fights money laundering.

In The New York Times interview, the president also said, "It's possible there's a condo or something... I sell a lot of condo units and somebody from Russia buys a condo, who knows." He also said he doesn't make money from Russia.