Mark Warner, the top Democrat on the Senate Intelligence Committee, is worried foreign governments are gaming search algorithms of social media sites like YouTube to serve up propaganda to manipulate American politics.

"Companies like YouTube have immense power and influence in shaping the media and content that users see," the Virginia senator said in a statement Monday. "I've been increasingly concerned that the recommendation engine algorithms behind platforms like YouTube are, at best, intrinsically flawed in optimizing for outrageous, salacious, and often fraudulent content."

"At worst, they can be highly susceptible to gaming and manipulation by bad actors, including foreign intelligence entities," he added.

Warner spoke out after a report was published in the Guardian newspaper Friday claiming YouTube's advertising algorithm automatically served up anti-Hillary Clinton videos six times more often than ones for Donald Trump in the lead up to the 2016 US presidential election. 

The Guardian reported that a former YouTube engineer named Guillaume Chaslot, who had been fired by Google in 2013, disclosed that the recommendation algorithm used by YouTube had been designed to deliberately amplify videos that are divisive, sensational and conspiratorial.  

Google denies this is the case.

"YouTube has sophisticated systems to detect and prevent manipulation of its platform, including its recommendation algorithms," the company said in a statement Monday.

Specifically, the company said that less than 5 percent of all YouTube views come from external sources like social media platforms, search engines and embeds. "Put simply, views from social networks do not have a significant impact on overall viewership," the company said.

The report comes as Google and other social media sites like Facebook and Twitter have been scrutinized in recent months by Congress after US intelligence agencies determined that the Russian government had used these platforms to disseminate false news and advertisements in an attempt to influence US elections in 2016. In November, representatives from Facebook, Google and Twitter testified before the Senate and House intelligence committees.

Google has said it has conducted a thorough investigation across all its products, including YouTube. The company says it's shared these findings with investigators. Accounts that were associated with the Russian government have been terminated, and related videos have been removed from YouTube, the company has said.

The company also says it uses a sophisticated spam and security-breach detection system to identify anomalous behavior, including any attempts to inflate view counts of videos or numbers of subscribers to game its recommendation algorithms.

"As we've reported to investigators, we've seen no evidence of manipulation by foreign actors," the company said.