US President Donald Trump has fired the State Department’s inspector general Steven Linick, who Democrats say was investigating US Secretary of State Mike Pompeo. In a letter sent to House Speaker Nancy Pelosi late on Friday, Mr Trump ordered the firing effective in 30 days. "It is vital that I have the fullest confidence in the appointees serving as Inspectors General. That is no longer the case with regard to this Inspector General,” he said. Ms Pelosi called the "late-night, weekend firing” an "acceleration of the President's dangerous pattern of retaliation against the patriotic public servants charged with conducting oversight on behalf of the American people”. An hour after the dismissal, Chairman of the House Foreign Affairs Committee Eliot Engel revealed that Mr Linick was investigating the head of the State Department, Mr Pompeo, for suspected abuse of office. "This firing is the outrageous act of a president trying to protect one of his most loyal supporters, the secretary of state, from accountability," Mr Engel, a Democrat, 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,” he added without providing details on the scope of the investigation. A Democratic aide told NPR that Mr Linick “was looking into the Secretary's misuse of a political appointee at the Department to perform personal tasks for himself and Mrs [Susan] Pompeo”. Senator Chris Murphy, a ranking member on the Senate Foreign Relations Committee, called for Senate action. “If Inspector General Linick was fired because he was conducting an investigation of conduct by Secretary Pompeo, the Senate cannot let this stand,” he said. A State Department spokesperson confirmed the firing to <em>The National</em>. US Ambassador Stephen Akard will be appointed to the position that Mr Linick had held since 2013. Mr Linick also briefed Congress behind closed doors during the impeachment process against Mr Trump. Since then, the president has fired several inspector generals. Last month, he fired Michael Atkinson, the inspector general for the intelligence community, and dismissed the acting inspector general at the Defence Department, Glenn Fine. Mr Fine had been tasked to oversee the allocation of the $2 trillion pandemic stimulus.