I-864 is used for immigrant visas like IR-1/ CR-1.
The K-1 visa is a nonimigrant visa and uses the I-134 form.
Here is the instructions from the embassy site in Moscow:
QUOTE
12. Financial documents from the petitioner – a US citizen: please note, that Affidavit of Support (form I-134) is not required, but may be requested. The document must be notarized. Please submit financial documents to show that the applicant will not become a public charge in the United States. Such documents may include, but are not limited to:
- Most recent year tax returns (form 1040) or tax transcripts from IRS
- Copy of bank account
- Earnings and leave statement
- W-2 forms
- Letter from employer
http://moscow.usembassy.gov/consular/consu...cord_id=fianceeEven though they say it is not required it is the best way to show that your fiance wont become a charge of the state. You need to prove that you are able to support your fiance and the I-134 is the best way.