WASHINGTON — President Donald Trump acknowledged for the first time Friday that he is under federal investigation as part of the expanding probe into Russia’s election meddling. He lashed out at a top Justice Department official overseeing the inquiry, reflecting his mounting frustration with the unrelenting controversy that has consumed his early presidency.

“I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt,” the president wrote on Twitter.

His morning missive apparently referred to Rod Rosenstein, the deputy attorney general whose role leading the federal investigation has become increasingly complicated. The White House has used a memo he wrote to justify Trump’s decision to fire FBI Director James Comey, but that Trump action may now be part of the probe. Thursday night, Rosenstein issued an unusual statement complaining about leaks in the case.

Trump advisers and confidants describe the president as increasingly angry over the investigation, yelling at television sets in the White House carrying coverage and insisting he is the target of a conspiracy to discredit — and potentially end — his presidency. Some of his ire is aimed at Rosenstein and investigative special counsel Robert Mueller, both of whom the president believes are biased against him, associates say.

Dianne Feinstein, top Democrat on the Senate Judiciary Committee, said she was “increasingly concerned” that Trump will fire both Mueller and Rosenstein.