In the case of a controlled foreign corporation, subpart F income does not include any item of income from sources within the United States which is effectively connected with the conduct by such corporation of a trade or business within the United States unless such item is exempt from taxation (or is subject to a reduced rate of tax) pursuant to a treaty obligation of the United States. For purposes of the preceding sentence, income described in paragraph (2) or (3) of section
921
(d) shall be treated as derived from sources within the United States. For purposes of this subsection, any exemption (or reduction) with respect to the tax imposed by section
884 shall not be taken into account.