In K-1 fiancée and K-3 visa cases, Packet 3/K Visa Instructions are available here. The documents and forms DS-160 for all applicants (including K-2 and K-4 who wish to travel with the principal applicant) in Packet 3 must be completed and/or obtained before a visa interview can take place.
Receipt of an I-797 Notice of Approval from U.S. Citizenship and Immigration Services (USCIS) does not indicate the case is pending with the U.S. Embassy. It takes approximately 2-6 weeks on average for approved cases to arrive at the Embassy. Once the U.S. Embassy receives an approved petition from NVC, the Immigrant Visa Unit will send a letter with specific instructions on requirements to prepare in order to process your K-1 application. If you do not receive instructions from the U.S Embassy within 2-6 weeks of receipt of a NVC notification on the transfer of your case to the embassy, you may email the consular section directly at IVPhnomPenh@state.gov.
Please do not send any documents to the Embassy unless you have been specifically instructed to do so by NVC or the U.S. Embassy. Any Immigrant visa documents sent to the U.S. Embassy for a case which is not currently pending at the U.S. Embassy will be destroyed.