The invitation letter is provided by the sponsor of the US visa to the visa applicant. The sponsor usually provides this letter to invite parents, relatives or guest to US. This letter is used as a supporting document during the interview.
The letter below is for reference only. Changes should be made as per your applicable situation.
I invite you to visit us and spend your vacation in USA with us. We have plan to visit famous tourist places like [name of tourist places to visit]. It will also be an opportunity for you to see and experience the American culture and lifestyle.
I will be taking care of your entire USA tour expenses, including the round trip air fare food, housing, medical insurance and all your other personal expenses.
Herewith I am sending all the required documents for getting the necessary tourist visa from the US Consulate, [Name of US Consulate]