In addition to the authority otherwise provided by the Inspector General Act of 1978 (
5 U.S.C. App.)
1 and in accordance with the requirements of this subsection, the Inspector General, in carrying out the provisions of this section, may require by subpoena the attendance and testimony of witnesses as necessary in the performance of the functions assigned to the Inspector General by the Inspector General Act of 1978 (
5 U.S.C. App.)
1 and this section, which in the case of contumacy or refusal to obey, such subpoena shall be enforceable by order of any appropriate district court of the United States.