As you may know, nonresident estate that is subject to tax is that which is real property and tangible personal property situated in the United States if physically located in the United States as well as intangible property that is located in the United States. An article for educational purposes on these concepts is at http://kmatzlaw.com/yahoo_site_admin/assets/docs/US_and_Gift_Taxation_of_Nonresident_Aliens_Updated.22861823.pdf
Shares in a U.S. corporation owned by a nonresident alien are specifically addressed in the tax code and therein deemed to be situated in the United States (regardless of where the certificates are physically located).
Similarly, shares in a foreign corporation are deemed situated outside of the United States regardless of where the certificates are located and regardless of where its assets are located. See IRC Section 2104(a).
However, there are no such specific code provisions for partnership interest locations.
Generally the IRS position uses the entity theory, such that a partnership would be treated as an entity for estate tax purposes and that entity would generally be situated where the partnership is engaged in business.
Since the issuance of the check-the-box regulations under section 7701 apply for all purposes of the code and the regulations themselves refer more than once to "federal tax purposes," (which would include estate and gift taxes) there seems to be every reason that all entities should be classified for transfer tax purposes just as they are for all other purposes under the section 7701 regulations. See Treas. Reg.301.7701-2
As is often the case, the application of federal tax regulations does depend on the the applicable local law. That is, if the partnership qualifies under local law as a separate and distinct legal entity, and when that partnership survives the death of one of its partners, then the entity treatment of where the partnership is engaged in business determines situs for transfer taxes.
Of course, we may need to engage local attorney assistance for these local legal issues. On the other hand, if the partnership is not recognized as a legal entity, or terminates upon the death of the partner, then situs of the location of the partnership interest is the location of the underlying partnership assets.
Also, Sweden is no longer one of the the different countries with which the United States has estate or gift tax treaties. So, no treaty has to be considered when determining the US estate tax situation of a resident of Sweden.
In summary from http://www.taxanalysts.com/www/features.nsf/Articles/EF4B18A62361343F8525792100546337 "Partnership interest situs rules come with significant uncertainty. The IRS ruled in Rev. Rul. 55-701, 1955-2 C.B. 836, that a partnership interest is located where the partnership business is carried out. However, the question of where the partnership business is carried out is one of facts and circumstances. Further, there are additional authorities that support a look-through to the partnership assets in order to determine whether they have a U.S. situs and therefore need to be included in the NRA estate. Thus, an NRA using a foreign partnership to invest in U.S.-situated assets subjects himself to U.S. estate tax exposure, particularly considering that partnership business location is based on facts and circumstances."
Yes, an investment in a fund, organized as a Delaware limited partnership, investing in U.S.shares can be considered as U.S. situs assets of a nonresident alien for U.S. estate tax purposes (when the facts are such that the partnership is an entity under local law and there is not any provision excluding such assets in the estate/gift tax treaty.)
Hope this helps even though there is uncertainty based on the facts.
Please ask if you need more discussion or clarification.