No, they are not an extension of the US. Actually, they are in direct opposition to US backed companies(agrobusinesses) in the region that want to plunder the natural resources there.

In Mexico, the ones that are actively supported by the US and serve as the "Freikorp" of capitalists are the narcos/drug traffickers. As evidence, you can see this quote from a lawyer of a union:

The intervention of organized crime groups in the country's mining sector "has become a cancer promoted by foreign capital, especially by Canadian and American companies," said Óscar Alzaga Sánchez, lawyer for the National Mining Union, which is chaired by legislator Napoleón Gómez Urrutia.

This is what I was trying to tell you by saying they stop internal plunder. This means that they are opposing those groups(promoted by national and US capitalists) to destroy the region.