A Mexican soldier keeps watch atop a military vehicle on June 12 outside a house used to store 20 tons of seized marijuana, in Tijuana, Mexico. (Jorge Duenes/Reuters)

After coming under fire, Mexican navy personnel in a Black Hawk helicopter shot back and killed six people near the U.S. border, authorities said Monday.

The shooting broke out Sunday in a rural area near Falcon Lake, a border-straddling reservoir on the Rio Grande, amid cattle ranches and tiny fishing towns. This stretch of border is where two drug cartels, the Jalisco New Generation and the Zetas, have reportedly been fighting.

The helicopter crew had been on patrol above an area known as El Cuatro when it approached a group of vehicles of suspected drug traffickers. According to the navy statement, the gunmen fired at the helicopter, striking it seven times, and the Black Hawk crew shot back and killed six people “among the group of aggressors.” The military released a video showing the bullet holes in parts of the helicopter.

The shootout took place about 20 miles from the U.S. border. Officials in Nuevo Laredo, the closest major city, as well as in the Tamaulipas state government and prosecutor’s office, said they had no further information about the incident.

Such silence is common in border towns where drug gangs are strong. The most prominent newspaper in Nuevo Laredo, El Mañana, did not cover the helicopter shooting. An editor said the paper does not write about such news anymore, given the threats and killings by cartel members that have muzzled many publications in dangerous parts of Mexico.

The No. 2 official in the nearby town of Nueva Ciudad Guerrero, Manuel Lopez Garza, said the shootout took place in an unpopulated area. He did not have much to add on the killings, either.

“They say we are the most insecure municipality in the state, but it’s not the truth,” he said.

He said it was common to see federal police and military patrols in the area. But he did not feel his town needed any reinforcements. “Each month, we have meetings with the people about security, and we don’t have reports of drug trafficking, shootouts, kidnappings, none of that,” he said.

Two months ago, suspected cartel members shot down a Mexican military helicopter in the western state of Jalisco with a rocket-propelled grenade. Six members of the military were killed in the May 1 attack. Authorities blamed the New Generation cartel, which has grown into one of the country’s most powerful drug gangs. The Jalisco state prosecutor, Luis Najera Gutierrez, stepped down from his post Monday, amid deteriorating security in the state.

During President Enrique Peña Nieto’s administration, the Mexican government has purchased at least 25 UH-60 Black Hawk helicopters, worth about $775 million, through the U.S. government's foreign military sales program. Some critics have expressed concerns that the military buildup — which includes thousands of Humvee trucks — will intensify the drug war, while officials say the sales have replaced old, outdated equipment .

Gabriela Martinez contributed to this report.