A new report says the vast majority of human rights abuses allegedly committed by Mexican soldiers in the country's war on drug gangs go unsolved and unpunished despite reforms letting civilian authorities investigate and prosecute such crimes.

The study by the Washington Office on Latin America found there were just 16 convictions of soldiers in Mexico's civilian judicial system out of 505 investigations from 2012 through 2016. That is a prosecutorial success rate of 3.2 percent.

Moreover, there were only two "chain of command responsibility" convictions for officers.

The report highlights factors that hinder civilian investigations of the military: parallel civilian and military probes, limited access to troops' testimony and soldiers tampering with crime scenes or giving false testimony.

There was no immediate government response to Tuesday's report.