If you plan to expand your Amazon business and start selling in the USA, getting a US trademark is a good idea since it would protect your intellectual property against infringement in the USA and also allow you to join the Amazon Brand Registry if you aren't already enrolled.
You can register a US trademark as a non-citizen; however, a licensed US attorney has to represent you. You can check out our offering for Amazon Brand Registry applicants, where we help business owners get a trademark in the US and other countries for the purpose of selling on Amazon.