WASHINGTON (REUTERS) - US Secretary of State Mike Pompeo on Wednesday (May 20) defended his recommendation the State Department's inspector-general be fired, saying he should have done it earlier, and rejected claims his decision was motivated by political retaliation.

However, Pompeo in a news conference declined to explain the rationale for the firing of Steve Linick, who congressional aides have said was probing whether Pompeo misused a taxpayer-funded political appointee to perform personal tasks for himself and his wife, such as walking their dog.

"In this case, I recommended to the president that Steve Linick be terminated. Frankly should have done it some time ago," he said, adding that he did not have information about any investigations Linick's office had been carrying out.

"There are claims that this was for retaliation, for some investigation that the inspector-general's office here was engaged in. Patently false. I have no sense of what investigations were taking place inside the inspector general's office," he said.

Democratic Senator Bob Menendez, the Republican-led Senate Foreign Relations Committee's ranking member, said Linick had been investigating Trump's declaration of a national emergency last year to clear the way for US$8 billion (S$11.3 billion) in military sales, mostly to Saudi Arabia, sidestepping congressional review.

"Crazy stuff," Pompeo said in response to the allegations, striking back at Menendez.

"This is all coming through the office of Senator Menendez.

"I don't get my ethics guidance from a man criminally prosecuted," he said.

Menendez was indicted on federal corruption charges in 2015.

The charges were eventually dropped by the Justice Department after a 2017 mistrial.

Menendez was later accused by the Senate Ethics Committee of accepting gifts and private flights from a wealthy friend in exchange for doing the friend favours in Washington.