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I hope this might be useful
221(g):
The document issued by the Department of State under Section 221(g) of the Immigration and Nationality Act (INA) is for the most part used for requesting additional information from the beneficiary such as missing documents, additional evidence, or advising them of not being able to issue their visa due to pending name/security checks i.e. Administrative Processing However, Section 221(g) is also used by the Department of State when returning petitions/applications to the USCIS for further review ultimately recommending revocation.
Why are Petitions/Applications Returned to the USCIS by an Embassy/Consulate Under Section 221(g)?
Petitions/applications are returned for a variety of case specific reasons. Returning a petition/application to the USCIS means that the embassy/consulate refuses to issue a visa to the beneficiary, but they do not have specific evidence to actually deny a visa application. So the next best thing to do is return the petition/application to the USCIS office where the petition was originally filed requesting further review and ultimately recommending revocation.
What Happens When a Petition/Application is Returned to the USCIS by an Embassy/Consulate?
• 221(g) is issued to beneficiary at conclusion of the interview stating the application and/or petition is being returned to the United States.
• Petition is returned to the United States by the interviewing consulate for "further review"
• Returned petition is received by the NVC. It is reviewed and entered into the fraud database by fraud management.
• Returned petition is sent to the local USCIS service center where the petition was originally filed and approved.
• Local service center receives returned petition.
• Local service center who processed the original petition sends a notice of receipt to the petitioner.
• Local service center reviews the returned petition and consular officer notes on the case.
• Local service center then sends either a NOID (Notice of Intent to Deny) or NOIR (Notice of Intent to Revoke) to the petitioner also asking for more proof of the relationship, many cases have specific consular objections to rebut.
• Petitioner is given 30-60 days from date of NOIR/NOID (depending on the service center) to respond with additional evidence of the relationship or other specific evidence. The timeframe to respond will be provided in the letter.
• Local service center receives evidence...if in the timeframe given (30-60 days) the case is reviewed and either original approval is reaffirmed or the petition is officially denied.
• If the petition is denied the local service center sends the petitioner an 'official' denial letter. This can be officially appealed if the denial letter states such.
• If the petition is reaffirmed the local service center sends the petitioner an official notice of reaffirmation.
• Local service center sends the reaffirmed petition AND its evidence provided in the rebuttal directly to the consulate along with a recommendation to issue a visa.
• Consulate notifies the beneficiary of a new interview date.
• Beneficiary has interview for the reaffirmed petition and the visa is either issued, or the case in placed in Administrative Processing which after cleared a visa is issued, or worst case scenario it is denied via Section 221(g) and returned again to the USCIS with a recommendation for revocation.

Here is a link for some interesting material for understanding the process
http://www.usaimmigrationattorney.com/SecurityNameChecksAndAdministrativeReview.html