Working overseas - can I contribute to my 401K?

[Anonymous]

I’m taking leave without pay from my current job (federal government) for 2-3 years. I will be working another job overseas with an international organization to which the U.S. is a representative member (think: UN, World Bank, WTO, WFP, WHO, etc). This new organization will pay me directly, I will no longer get a paycheck from the U.S. government.

What are my options for retirement investments? Is it possible to still contribute to my thrift despite not receiving any monies from the U.S. government? Am I better off opening a self-directed 401K for a few years? Or is that not even allowed with foreign sourced income?

Thanks!!!