Former Massachusetts Gov. Mitt Romney said Thursday that Russian-linked donations to Hillary Clinton's family foundation make it appear as if the Democratic presidential candidate "was bribed" while serving as secretary of state.

"You know, I've got to tell you, I was stunned by it. I mean, it looks like bribery," the former Republican presidential nominee told radio show host Hugh Hewitt, reported The Washington Times. "I mean, there is every appearance that Hillary Clinton was bribed to grease the sale of, what, 20 percent of America's uranium production to Russia, and then it was covered up by lying about a meeting at her home with the principals, and by erasing emails."

Romney was referring to a report published by The New York Times on Thursday which alleged that, in exchange for $2.35 million in donations to the Clinton Foundation, Clinton's State Department approved a number of deals which enabled Russia's atomic energy agency, Rosatom, to take control of one-fifth of the uranium produced in the U.S.

"And you know, I presume we might know for sure whether there was or was not bribery if she hadn't wiped out thousands of emails," Romney added. "But this is a very, very serious series of facts, and it looks like bribery."

The Times, reporting on story lines found in the upcoming "Clinton Cash" book set to be released May 5, revealed that shortly after the Russians announced plans to go through with the acquisition of the mining company, Uranium One, a Russian investment bank with ties to the Kremlin paid former President Bill Clinton $500,000 to give a speech in Moscow.

ABC News reported that the former president typically drew $150,000 for speeches in the years following his presidency, but after his wife accepted a job at the State Department, those speaking fees doubled or tripled.

"Their assets are comingled. This is the same thing as if a half a million dollars went to Hillary Clinton," Romney said. "And as secretary of state, you just can't have foreign governments or groups that are associated with foreign governments, or fronts for foreign governments, giving money to the United States secretary of state. This, you know, her responsibility as secretary of state is the centerpiece of her presidential campaign. And at best, it's an ethical morass. That's at best."

Clinton's campaign team has denounced the report as little more than "absurd right-wing conspiracy theories" based on "sloppy research."

"The bottom line remains that the book fails to produce a shred of evidence supporting the theory that Hillary Clinton ever took action as secretary of state for the purposes of supporting the interests of donors to the Clinton foundation," campaign spokesman Brian Fallon wrote in a memo, according to The Washington Times.

Romney said that in order for Clinton to reassure the public that she committed no wrongdoings, she will likely have to release her tax returns, something he refused to do during his 2012 presidential bid.

"Well, no question if she runs for president, Bill and Hillary Clinton will have to release their joint returns, not just her return, but their joint returns, because assets are commingled," he said. "And No. 2, yes, the Foundation would have to release its returns as well. I'm not asking for 10 years, but I'm saying they ought to give at least three years of returns so we can see where the money's been coming from."