How to cite a letter from the Ministry of Health in APA Style?
If the letter is available to the public via a website, you could treat the letter as a free-standing web resource and note the URL in the reference, versus noting a repository as a source. If you refer to pages 212-213 in the Publication Manual of the American Psychological Association (American Psychological Association, 2010), you'll find information on how to reference letters. Please adapt one of the examples there to best suit your resource, keeping in mind that the point of the reference is to direct your reader to the resource. If the letter isn't publicly available, please use the format for personal communication and note the Ministry of Health as the author of the communication.
American Psychological Association. (2010). Publication manual of the American Psychological Association (6th ed.). Washington, DC: Author.