I have been to Thailand several times and would like to purchace a condo near the water. I am an American citizen, paying american taxes, and was wondering if I am able to deduct the mortgage interest on my U.S. taxes.

You didn't provide enough information to give a concise answer. Will you be living in the unit? Will you be renting it out?

In general, however, the rules for mortgage interest deduction do not depend on the property being in the US. If the property qualifies as your principal residence or as a second home, the usual limitations apply.

If you operate the property as a rental, you must report the income and may deduct the related expenses, including interest.