26 U.S.C. § 2511: Transfers in general

(a) ScopeSubject to the limitations contained in this chapter, the tax imposed by section 2501 shall apply whether the transfer is in trust or otherwise, whether the gift is direct or indirect, and whether the property is real or personal, tangible or intangible; but in the case of a nonresident not a citizen of the United States, shall apply to a transfer only if the property is situated within the United States. (b) Intangible propertyFor purposes of this chapter, in the case of a nonresident not a citizen of the United States who is excepted from the application of section 2501(a)(2)—(1) shares of stock issued by a domestic corporation, and (2) debt obligations of—(A) a United States person, or (B) the United States, a State or any political subdivision thereof, or the District of Columbia, which are owned and held by such nonresident shall be deemed to be property situated within the United States.