Sochi Olympics whistleblower threatened: "You will be drowned in blood."

Fourth-Place Medal

Allegations of corruption behind the costliest Winter Olympics took a twist when a Russian whistleblower told ABC News that he is a “marked man.”

“You will be drowned in blood,” government officials supposedly told Russian businessman Valery Morozov after he publicly made allegations of corruption surrounding the Sochi Olympics.

In the interview, which will air tonight on ABC News' "World News With Diane Sawyer" and "Nightline,” Morozov said he fled to Great Britain for fear of his life. The former construction executive also said he believes an attempt on his life will likely be made after the Games end in late February.

Morozov’s revelation comes amid criticism of the cost of the Olympics—estimated at $51 billion—which was bloated by construction cost overruns, according to reports.

Russian President Vladimir Putin denies such allegations and welcomes anyone with evidence to come forward.

"We don't see any large-scale instances of corruption during our preparations Sochi. If anyone has any information about corruption in Sochi, please hand it over, we will be glad and grateful," Putin said in an interview with ABC, BBC and Russian and Chinese journalists broadcast on Sunday.

[ Related: Russian activist publishes Sochi corruption file. ]

On Monday, anti-corruption activist Alexei Navalny launched an interactive website illustrating how construction money was spent in and around Sochi.

Navalny says Russian contractors spent twice the cost to build some of the Olympic venues, including the Bolshoi Ice Palace, the Fisht Stadium for the opening/closing ceremonies and the speed-skating arena.

The International Olympic Committee says allegations of corruption are out of its jurisdiction, and that it is the responsibility of the Russian government to handle such charges, according to ABC News.

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