Here is the IRS instructions -- this is only applicable for US citizens/Resident( GreenCard ) and only when residing in the USA:
If you are a U.S. citizen working in the United States for a foreign government or international organization, you must report this compensation as wages on Form 1040 and pay self-employment tax on the compensation under the Self-Employment Contributions Act (SECA). Self-employment tax is computed on Schedule SE, Self-Employment Tax, and is also reported on Form 1040. Although you are subject to self-employment tax on this employee compensation, you are not "self-employed" for any other federal tax purposes. You may not claim deductions for expenses on Schedule C and are not qualified to establish a Simplified Employee Pension (SEP) Plan and there is no allowable deduction for contributions to any such plan. Rules of contributing to SEP/IRA plans are explained in IRS Publication 560, Retirement Plans for Small Business, and Revenue Ruling 73-384 for additional information.
So the easiest way is to report the 1099-MISC on schedule-C just the gross income and no expenses. So it would compute the SECA properly and transfer everything to form 1040. I think some of the international organizations compensation may be exempt from Fed and Sate taxes ( but SECA is required) while for others they do withhold federal taxes. But I believe World Bank is one of those covered by executive order .
