WASHINGTON — Deputy Attorney General Rod Rosenstein issued a statement late Thursday night that warned Americans to “be skeptical” of stories based on anonymous sources after reports in recent days about the focus of special counsel Robert Mueller’s investigation.

Rosenstein, who appointed Mueller to investigate Russian interference in last year’s election and whether the Trump campaign coordinated with Russia, sent out the warning in an email at about 9:30 p.m. without saying what prompted him to take that unusual step.

The statement also came several hours after President Donald Trump posted several tweets complaining about Mueller’s investigation. Trump picked up that theme again Friday morning, tweeting: “After 7 months of investigations & committee hearings about my ‘collusion with the Russians,’ nobody has been able to show any proof. Sad!”

Rosenstein’s statement in full said:

“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. The Department of Justice has a long-established policy to neither confirm nor deny such allegations.”

Rosenstein became the Justice Department official overseeing the investigations into the Russia election meddling and Trump after Attorney General Jeff Sessions recused himself from any matters arising from the 2016 presidential campaigns because he served as a prominent Trump campaign adviser.

advertisement | advertise on newsday

A spokesman for the Justice Department did not respond to an email request for clarification and comment Friday morning.

“We’ll decline to comment on the ongoing investigation,” said Peter Carr, a spokesman for the special counsel.

Rosenstein’s statement appeared just hours after The Washington Post reported Mueller is looking into the business dealings of Jared Kushner, President Trump’s adviser and son-in-law, based on unnamed American sources.

On Wednesday the Post reported that five unnamed sources said Mueller is investigating whether Trump obstructed justice by seeking to end a probe of a former top national security adviser and firing FBI Director James Comey, The New York Times used unnamed sources to report that Mueller had requested interviews with three top intelligence officials.