AIS will issue a letter of invitation, if you need a USA Visa.
If you are a citizen of a country listed in the USA visa waiver program, or you currently hold a valid visa to the United States, you do not need to request a visa invitation letter from AIS.
Provided that you need an invitation letter to receive a visa to participate in the conference, you must send the following information to firstname.lastname@example.org.
1) First and last names as they appear on your passport
2) Country of citizenship
3) Passport number
5) Home address
6) Phone number
7) Email address
Check this link for the list of the countries in the U.S.A. visa waiver program.
Check this link for information about your visa application.