RUN to a tax professional or tax lawyer who is familiar with the U.S. tax treatment of pensions from your country. I say run because you might have a limited amount of time to avoid or defer paying tax on the lump sum, perhaps as little as 60 days. The options are different for different countries, and might depend on a tax treaty between the U.S. and the other country. This is not a do-it-yourself project. You need an expert with specialized knowledge. The expert that you consult will be able to tell you how to report the lump sum.
