(CNN) A criminal gang used a high-caliber rifle to bring down a helicopter in southern Mexico, said the country's national security commissioner, Renato Sales.
Sales told Radio Formula on Wednesday that the helicopter was attacked Tuesday in the state of Michoacan with a Barrett .50-caliber rifle. The National Security Commission is working with state authorities to find the people responsible, Sales said.
The attack killed four people on board the helicopter during an operation to capture "criminal cells" in the area around Apatzingan, which is an area hard to reach by land, according to Michoacan Gov. Silvano Aureoles.
It was not immediately clear how authorities had determined the caliber of rifle used in the attack. On Tuesday there were mixed reports on whether the helicopter was shot down or had crashed accidentally.
A survivor of the crash is in intensive care, and will be a crucial witness in the investigation, the governor said.
Michoacan has long been a flash point in Mexico's drug war, and battles between criminals and security forces are common.
In May 2015, a shootout left 42 gunmen and one federal police officer dead.
In July, the mayor of Pungarabato, a small town in Mexico's Guerrero state, was killed in a shooting on a highway in Michoacan.