You don't need to report it to the U.S. at all. When you sell it, you don't need to report the gains to the U.S. if they were under $100k.
Here is some more info for you:
FBAR (Foreign Bank Account Report)
If you have over $10,000 in foreign financial accounts at any time during the year, you must file an FBAR. While there’s no tax liability involved, there are steep penalties for not filing.
Filing an FBAR means filing FinCEN Form 114 online:
https://bsaefiling.fincen.treas.gov/NoRegFBARFiler.html
FATCA (Foreign Account Tax Compliance Act) Form 8938
Expats with a total value of foreign assets (excluding real estate) exceeding $400,000 also have to report them on IRS Form 8938 with your tax return.
https://www.goldinglawyers.com/form-8938-real-estate-irs-basics-of-foreign-real-estate-reporting/
https://www.irs.gov/businesses/corporations/fatca-information-for-individuals
When selling foreign property, only need to tell the IRS if capital gains are over $100k. If they are, fill out Form 3520. If the foreign property was your personal residence, you may be eligible for exclusion of your gain on your US tax return if you meet the 2 years out of 5 test for residing in the home.
