You can add a FAA IR to the US "restricted " license based on a foreign license.
It will read " US Instrument test passed".
When this licence is issued, there will be a letter that accompanies it. This letter has a 6 month expiration. If you do a FAR 141 IR (not a part61) within this time frame, you can then add an the rating to your certificate.
Close, it does not have to be a Part 141 Instrument rating.
However, Instrument training requires a M-1 visa and only 14 CFR Part 141 certified schools can issue the I-20, which is the form you need to go to the US embassy and apply for the visa.
It does not mean that you have to do your training part 141, it can be part 61.
Everything you do involving a foreign license needs to be accompanied by the letter of verification.
Read about it on the FAA website:
http://www.faa.gov/licenses_certific..._verification/