President Donald Trump tweeted on Friday that he is under investigation, an apparent reference to the probe into Russia's involvement in the 2016 presidential election.

He also appeared to criticize Deputy Attorney General Rod Rosenstein, who appointed a special counsel to oversee the investigation.

@realDonaldTrump: I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt

Sources close to the president's outside legal counsel told NBC News that Trump was not confirming the investigation. Instead, the sources said he was referencing a Washington Post story published Wednesday night.

The Washington Post reported special counsel Robert Mueller is seeking to determine whether Trump attempted to obstruct justice, following the president's firing of former FBI Director James Comey, who had been leading the investigation of Russian interference.

Rosenstein wrote the memo that suggested that Trump fire Comey over his handling of an investigation into Hillary Clinton's use of a private email server while secretary of State. Trump later contradicted his administration's rationale, saying he had been thinking about the Russia investigation when he fired Comey.

In a striking testimony before Congress last week, Comey said he believed Trump had sought to persuade him to drop an investigation into then National Security Advisor Michael Flynn's ties to Russia.

If Trump did in fact intend to criticize Rosenstein, it would not be the first time he has publicly scolded his Justice Department. Last week, he tweeted that the department should not have revised an order banning people from several Muslim-majority nations from entering the United States.

Trump's apparent acknowledgement of the reported obstruction of justice investigation came after a series of tweets in which he renewed his assertions that he is the subject of a "witch hunt."

@realDonaldTrump: After 7 months of investigations & committee hearings about my "collusion with the Russians," nobody has been able to show any proof. Sad!

@realDonaldTrump: The Fake News Media hates when I use what has turned out to be my very powerful Social Media - over 100 million people! I can go around them

@realDonaldTrump: Despite the phony Witch Hunt going on in America, the economic & jobs numbers are great. Regulations way down, jobs and enthusiasm way up!

The Washington Post cited unidentified officials when it reported Mueller is investigating Trump. Rosenstein issued a statement on Thursday warning Americans to "be skeptical of anonymous allegations."

"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," Rosenstein said.

A senior Justice Department official told NBC News that no one pushed Rosenstein to issue the statement.

"This was 100 percent Rod. He's tired of reading all these stories based on anonymous sources claiming to know what the Justice Department and the FBI are doing," the official said.

— CNBC's Christine Wang contributed to this story.

Correction: This story was revised to correct that Comey testified last week.

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