Treas. Reg. § 1.404(a)-11

In order that a trust may constitute a qualified trust under section 401(a) and be exempt under section 501(a), it must be created or organized in the United States and maintained at all times as a domestic trust. See paragraph (a) of § 1.401-1. Paragraph (4) of section 404(a) provides, however, that an employer which is a resident, a corporation, or other entity of the United States, making contributions to a foreign stock bonus, pension, or profit-sharing trust, shall be allowed deductions for such contributions, under the applicable conditions and within the prescribed limits of section 404(a), if such foreign trust would qualify for exemption under section 501(a) except for the fact that it is a trust created, organized, or maintained outside the United States. Moreover, if a nonresident alien individual, foreign corporation, or other entity is engaged in trade or business within the United States and makes contributions to a foreign stock bonus, pension, or profit-sharing trust, which would qualify under section 401(a) and be exempt under section 501(a) except that it is created, organized, or maintained outside the United States, such contributions are deductible subject to the conditions and limitations of section 404(a) and to the extent allowed by section 873 or 882(c).