Mexico City: Mexico`s army pledged Friday to cooperate in an investigation into the deaths of 21 gang suspects after a witness claimed that soldiers executed them, contradicting official reports they died in a shootout.
The defense ministry said in a statement that it would offer its "unrestricted collaboration to the appropriate authorities to shed light on the facts."
"This entity is the most interested in seeing this incident thoroughly investigated," it said.
The US State Department, whose government has provided more than $1 billion in training and equipment to Mexico`s security forces in the drug war, called for a "credible review" to be conducted by civilian authorities.
The Latin America edition of US magazine Esquire reported this week that it had interviewed a woman who saw the soldiers kill the suspects after they surrendered following a shootout.
In a statement following the June 30 skirmish, the defense ministry said the drug gang suspects shot first from a warehouse while the soldiers were on a night patrol in the town of Tlatlaya, 240 kilometers (150 miles) southwest of Mexico City.
The statement said 21 men and one woman were killed and a soldier was injured in a gunfight, and that three women who presented themselves as kidnap victims were rescued.
Esquire said the witness is one of the three women but she denies she was kidnapped.
The woman said only one person was killed during the shootout, while the 21 others were executed after they were interrogated, the magazine reported.
The woman said one of those killed was a 15-year-old girl.
The defense ministry`s statement on Friday reiterated that the soldiers repelled an armed assault, but it gave no further details about the event.
Global human rights group Amnesty International called for an "exhaustive and impartial investigation" into the deaths.
Human Rights Watch said the witness`s account would make the deaths the "worst massacre of civilians by soldiers" in the administration of President Enrique Pena Nieto, who took office in 2012.
The armed forces have been dogged by abuse allegations ever since then president Felipe Calderon deployed troops to crack down on drug cartels in December 2006.
The attorney general`s office issued a statement saying it was still investigating the case and that the probe would be "complete and thorough to get to the truth."