Here is a letter (actually an email) which was forwarded to me from a congressman's office who has been only partially- helpful in expediting my K1.
"The case is currently pending receipt of required clearances. This involves an interagency process that takes place in Washington, D.C. Once we receive the clearances, we will contact the applicant to continue processing her case."
"As a result of enhanced homeland security, visa applications are now subject to a greater degree of scrutiny than in the past. We regret if this may have resulted in some inconvenience for the petitioner and the applicant. Please be assured that we will process the visa application to conclusion as expeditiously as the law will permit."
Moral: don't be surprised if your K1 visa suddenly gets stalled after the interview!
