US President Donald Trump has fired the State Department’s inspector general, an Obama administration appointee whose office was critical of alleged political bias in the department’s management.

The sacking is the latest in a series of moves against independent executive branch watchdogs who have found fault with the Trump administration.

A senior department official said Mr Trump removed Steve Linick from his job on Friday but gave no reason for his dismissal.

In a letter to Congress, Mr Trump said Linick, who had held the job since 2013, no longer had his full confidence and that his removal would take effect in 30 days.

Mr Trump did not mention Linick by name in his letter.

Democrats in Congress immediately cried foul, with the chairman of the House Foreign Affairs Committee suggesting Mr Linick was fired in part in retaliation for opening an unspecified investigation into Secretary of State Mike Pompeo.

“This firing is the outrageous act of a president trying to protect one of his most loyal supporters, the secretary of state, from accountability,” New York Democrat Eliot Engel said in a statement.

“I have learned that the Office of the Inspector General had opened an investigation into Secretary Pompeo. Mr Linick’s firing amid such a probe strongly suggests that this is an unlawful act of retaliation.”

Mr Engel offered no details of the alleged investigation into Mr Pompeo, but Mr Linick’s office had issued several reports critical of the department’s handling of personnel matters, including accusing some of Mr Trump’s appointees of retaliating against career officials.

House Speaker Nancy Pelosi also condemned Mr Linick’s removal, saying he had been “punished for honourably performing his duty to protect the Constitution and our national security”.

“The president must cease his pattern of reprisal and retaliation against the public servants who are working to keep Americans safe, particularly during this time of global emergency.”

Mr Linick will be replaced by Stephen Akard, a former career foreign service officer who has close ties to Vice President Mike Pence, according to the state department official who spoke to The Associated Press on condition of anonymity.

Mr Akard currently runs the department’s Office of Foreign Missions. He had been nominated to be the director general of the foreign service but withdrew after objections he was not experienced enough.

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Secretary of State Mike Pompeo, who is said to be the topic of an investigation opened by Steve Linick (Andrew Harnik/AP)

Mr Linick, a former assistant US attorney in California and Virginia, had overseen inspector general reports that were highly critical of the department’s management policies during the Trump administration.

His office had criticised several Trump appointees for their treatment of career staff for apparently being insufficiently supportive of Mr Trump and his policies.

Under Mr Linick, the State Department’s inspector general office was also critical of former Secretary of State Rex Tillerson’s hiring freeze and attempts to streamline the agency by slashing its funding and personnel.

Mr Trump has been taking aim lately at inspectors general.

In April, he fired Michael Atkinson, the inspector general for the intelligence community, for his role in the whistleblower complaint that led to Mr Trump’s impeachment.

Mr Trump then removed Glenn Fine as acting inspector general at the Defence Department, a move that stripped him of his post as chairman of the Pandemic Response Accountability Committee.

During a White House coronavirus briefing, Mr Trump questioned the independence of an inspector general of the Department of Health and Human Services over a report that said there was a shortage of supplies and testing at hospitals.