Deputy Attorney General Rod Rosenstein is telling Americans to be "skeptical" of news stories that use anonymous sources.

"Americans should exercise caution before accepting as true any stories attributed to anonymous ‘officials,' particularly when they do not identify the country — let alone the branch or agency of government — with which the alleged sources supposedly are affiliated. Americans should be skeptical about anonymous allegations," said Rosenstein in a late Thursday statement.

He added: "The Department of Justice has a long-established policy to neither confirm nor deny such allegations."

Rosenstein's statement didn't refer to any specific news story, but less than 24 hours prior, The Washington Post reported that Robert Mueller, the FBI's special counsel investigating Russian meddling in the 2016 election, is investigating President Trump for possible obstruction of justice.

Trump called the report "phony" in a Thursday morning tweet.

Rosenstein appointed Mueller to be the special counsel of the Russia investigation after he took over the probe following a recusal by Attorney General Jeff Sessions in March.