A terse White House announcement said on Thursday that his nomination sent to the Senate, which has to approve the appointment, was being withdrawn and gave no reason for it.
The top position in the State Department overseeing South Asia affairs has not been filled since Nisha Biswal quit after Trump became President in 2017. A career diplomat, Alice Wells, has been looking after the portfolio on an acting basis.
The Washington Examiner, a conservative publication, said that according to a senior administration official Williams had decided not to pursue the job. It said he cited "family reasons" for the decision.
Scores of diplomatic positions are unfilled. The US does not have an ambassador in Pakistan after David Hale moved to Washington to become the under secretary of state for political affairs in August.
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