The nearest US embassy or consulate. Generally, you should not have to pay any US taxes if your country of residence has higher tax rates than you would pay in the US. The amount of foreign taxes above the US amount can be declared as a carry forward deduction. That would come into play if you moved back to the US. I forget how many years you can carry forward but it is several.If the country of residence has lower taxes, you may be liable for some taxes, but under the IRS rules, when you live abroad for a soecific amount of time, you can exempt a sizeable amount of income from US taxation.The US Consulate should have all the forms and instructions you need.