5 U.S.C. § 5913

(a) For the purpose of this section, “agency” has the meaning given it by section 5721 of this title . (b) Under such regulations as the President may prescribe, funds available to an agency for administrative expenses may be allotted to posts in foreign countries to defray the unusual expenses incident to the operation and maintenance of official residences suitable for— (1) the chief representatives of the United States at the posts; and (2) such other senior officials of the Government of the United States as the President may designate. (c) Funds made available under subsection (b) may be provided in advance to persons eligible to receive reimbursements.