Hillary Clinton's campaign manager Sunday charged Donald Trump with potentially being a "puppet" of the Kremlin and demanded that the Republican presidential nominee disclose whether members of his campaign are conducting meetings with Russian officials.

"Paul Manafort has been pushed out, but that doesn't mean that the Russians have been pushed out of this campaign," Robby Mook told ABC's George Stephanopoulos. Mook was referring to the recent departure of Trump's campaign manager, whose consulting firm is now being investigated by the FBI and Justice Department for possible ties to corruption involving ousted Ukrainian President Viktor Yanukovych.

"The hand of the Kremlin has been at work in this campaign for some time," Mook continued. "It's clear that they are supporting Donald Trump, but we now need Donald Trump to explain to us the extent to which the hand of the Kremlin is at the core of his own campaign."

Mook claimed there are "real questions being raised about whether Donald Trump himself is just a puppet for the Kremlin in this race," citing his previous praise of Russian President Vladimir Putin and attitude toward NATO.

"We've seen, over the last few weeks, him parroting Vladimir Putin in his own remarks. We saw Donald Trump talk about leaving NATO and leaving our Eastern European allies vulnerable to a Russian attack," he said. "There are a lot of questions here and we need Donald Trump to disclose all of his financial ties and whether his advisers are having meetings with the Kremlin."

Mook has previously suggested that Russian officials were behind last month's hacking and subsequent release of Democratic National Committee emails, claiming that the U.S. adversary wants to see Trump make it to the White House.