An Algerian national with US citizenship (duel citizenship). He was recruited and employed by the Algerian branch office of a US company. In the eyes of the Algerian labor authorities the employee is a local Algerian hire and therefore the U.S. company’s branch office has been withholding and paying local taxes and social security (social health) on the employee’s behalf. The employee has been filing a U.S. tax return since returning to Algeria from the U.S. five years ago. The employee has also been making annual 15+% FICA payments with each tax return. There is no tax treaty between the US and Algeria. What obligation does the employer have in making FICA payments on the employee’s behalf?

That's a very good question.

I suggest you go to this site;
Social Security International Operations (http://www.socialsecurity.gov/foreign/index.html)
And contact the SSA at the numbers suggested.