The woman was shot dead last month during unrest at a dam in Chihuahua state near the US border.

"Six arrest warrants were carried out against the personnel involved ... in respect for human rights," the National Guard said on Twitter, having previously called the death an "unfortunate accident."

Farmers occupied the La Boquilla dam in Chihuahua in early September, saying they feared a drought would ruin their crops.

Under a pact dating back to 1944, the neighboring countries share water from two major rivers flowing from the southwestern United States to Mexico, the Colorado and the Rio Grande.

The United States complained last month that its neighbor owed almost a year's worth of water needed for crop irrigation, municipal water supplies and industry.

Mexico said last week it had reached an agreement to settle the debt in return for a commitment from the United States to provide water in the event of shortages.