Sanctions won’t work, but tanks would.
The entirety of Myanmar's army stock of modern armoured vehicles is less than 1000, with only 200 modern tanks in unknown state of readiness.
3-4 marine heavy brigades can easily stomp all tank battalions in Myanmar's disposal.
Just saying it to state that if US wants to do anything about that, it can do that effortlessly much like its Grenada, and Panama interventions.
Laos, and Vietnam will also be eager to trim ambitions of their bellicose neighbour.
The question is how Washington, and countries in the region are afraid the prospect of direct encounter with Chinese military which is rumoured to have a secret military treaty with Yangon.