How to block countries on a Facebook group?

Hello. I am an administrator of several donation groups on Facebook, and one of them is exclusively for France/Belgium. I regularly receive posts that I delete and ban people from, coming from Africa, Algeria, Canada, etc. I would simply like to be able to set keywords that will prevent these posts from appearing in the group. I've looked but I don't see anything. I can switch the group to private. But does anyone have an idea of how to possibly do this and if the option exists? Thank you all for any responses that will be provided.