Hello again Helmut,
I apologize for not explaining my answer entirely.
The answer is yes, you may deduct the interest on your mortgage which you pay to a foreign bank, BUT, only if you have done one of two things:
1. Either withhold 30% in tax from the interest portion of your payment OR
2. Obtain a signed W-8BEN form from the lender showing they are exempt from this withholding
You would of course not need to do either of these things simply to claim the interest as a deduction
. However, if the IRS were ever to select your return for an audit, if you had not complied with one of the above two rules
, then your interest deduction would end up being disallowed.
Thank you Helmut, and let me know if you have more questions.