Mexico's Defense Department says its troops were instructed to have "unrestricted" respect for human rights a year ago when soldiers allegedly killed at least 12 suspected drug gang members after they had surrendered.

The statement issued late Friday was the army's first response to the documents released by the Miguel Agustin Pro Human Rights center showing that high-ranking officers had given Mexican soldiers standing orders to "kill criminals."

Orders signed June 11 by Lt. Col. Sandro Diaz Rodriguez, on behalf of the command of the 102 Infantry Battalion, said "soldiers should operate on a mass scale at night and reduce daytime activities, with the aim of killing criminals at night."

Friday's statement never addressed the exact quote, but said the standing orders included "38 indications protecting human life, security of the troops and a focus on protecting human rights."

The human rights group said the government's response was inadequate.

The killings took place on June 30, 2014, in the municipality of Tlatlaya in Mexico State.