If the individuals who own both the LLC and foreign corporations are nonresident aliens, the LLC cannot elect to be an s-corp. Since a 1065 is filed, our understanding is that it is treated as a partnership rather than c-corp, as Bill says.
Your response doesn't indicate that the foreign corp owns the US LLC (which is treated as a partnership) or the other way around, just that both entities are under common control of these nonresident aliens - if the LLC is a c-corp, the compliance and disclosure requirements would be different.
Absent any business relationship or agreement, there is no basis for the US LLC to pay the mortgage interest for which the foreign corp is liable nor should the US LLC then be able to take a deduction. The foreign corp should have filed a W-8BEN-E or W-8ECI with the tenant. US-ECI would also trigger a filing requirement for 1120-F.
Your question says the mortgage is on the land and you talked about depreciation not being applicable on land. If you imply that there's rental income, it is generally subject to US tax on a gross rather than net basis unless an election is made to treat that as US-ECI. NRA's are also subject to withholdings and FIRPTA.
You also mentioned that a F.3520 may be needed but there is no indication that a trust is involved and why you believe it is necessary.
The facts you presented are quite confusing. You may like to review the these and the technicalities in greater details.
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Still an AllStar
