Mexican authorities say they have seized two farms that were being used to assemble semi-automatic rifles.

At least some of the AR-15 parts are believed to have been brought in from the United States, and then the rifles were put together in Mexico.

Jalisco State Prosecutor Luis Carlos Najera says four people have been detained and 18 weapons seized. He estimates that around 100 weapons may have been produced.

Najera said Tuesday that investigators believe the operation supplied arms to buyers in the state of Michoacan and also the local Jalisco New Generation Cartel.

Authorities seized equipment he described as "highly sophisticated machinery" designed to ensure the weapons function properly.