MEXICO CITY – Mexican soldiers shot two children in April in their family’s vehicle, and apparently altered the crime scene to try to blame the deaths on drug cartel gunmen, Mexico’s National Human Rights Commission said Wednesday.

The conclusions of the governmental commission represent one of the strongest condemnations to date of the Mexican army.

While soldiers have frequently been accused of human rights abuses since the army took on a leading role in fighting drug cartels in late 2006, the report suggests the military also engaged in an elaborate cover-up in the deaths of the boys, aged 5 and 9.

The Defense Department press office said it had no immediate comment.

After the boys’ mother said soldiers shot her sons with rifles, the army said in late April that its own study concluded the boys were killed by fragments from a self-propelled grenade of a type it doesn’t use.

The rights commission’s president, Raul Plascencia, said the Defense Department’s study “is unfounded and does not agree with the evidence.”

Thirteen members of the family were traveling in the vehicle April 3 in an area where the Defense Department said soldiers were pursing a convoy of gunmen in the northern state of Tamaulipas. It said the family got caught in crossfire during the confrontation, in which five other members of the family were wounded.

Plascencia said the evidence suggests additional rounds were later fired into the family’s vehicle to make it look more like a crossfire incident. The army – which immediately took charge of the scene of the shooting – also apparently planted two vehicles at the scene that witnesses said had not been there at the time of the shooting, he said.

The evidence suggests “an arbitrary use of public force,” Plascencia said.

The commission formally recommended that authorities reinvestigate the case, punish those responsible and submit soldiers to periodic psychological tests. The recommendations are not binding.

Tamaulipas has been the scene of bloody battles between drug cartels and security forces. Such violence has cost more than 23,000 lives nationwide since President Felipe Calderon took office in December 2006 and launched an offensive against the cartels.

Calderon has said the army is putting greater attention on ensuring troops respect human rights. But critics say the army should not be involved in law enforcement tasks and complain the current system allows soldiers to be investigated and tried in military courts, rather than civilian ones.