At least nine U.S. citizens — including six children — were killed in what local media described as a highway ambush in the Mexican border state of Sonora late Monday, a family member told NBC News.
The dead included 8-month-old twins, said Kendra Lee Miller, who is related to many of the victims. There were at least eight survivors.
Miller added that the victims lived in La Mora, which is about 75 miles south of the U.S. border.
Miller named the victims as Christina Marie Langford Johnson, 29, Dawna Langford, 43, and Trevor Langford, 11, and Rogan Langford, two-and-a-half. Also slain were Rhonita Miller, 30, Howard Miller, 12, Krystal Miller, 10, and eight-month-old twins, Titus and Tiana Miller.
Earlier another relative of one of the victims, Willie Jessop, told NBC News on the phone out of Utah overnight that a number of people were traveling in a motorcade consisting of several families when they came under the attack.
Jessop said three of the cars were shot at and one of them was set on fire based on the information he has been receiving from other family members at the scene.
Jessop said they have been trying to mobilize Mexican federal officials and have been in contact with the FBI.
“Everyone is in so much shock," he said. "It's just unbelievable and there's just no way to comprehend it."
Mexico has been hit by a wave of attacks in recent weeks, shocking even for a country used to more than a decade of intense drug war violence. The most notable incident was a military-style cartel assault that forced the government to release a leader of the Sinaloa Cartel in October.
Monday's incident may increase pressure on President Andres Manuel Lopez Obrador to crack down on armed groups.
El Universal, one of Mexico's largest newspapers, quoted other relatives as saying that members of a Mormon family were killed in what appeared to be an organized crime ambush.
There was no immediate indication of who was behind the attack.
El Universal reported that a large group of family members were traveling to La Mora, in the municipality of Bavispe, from another part of the municipality when they were ambushed.
Mexico's national civil defense agency confirmed that elements of the National Guard, the army and the state police were conducting a search operation in Bavispe on Monday night in response to the reports. It provided no other information.
The U.S. Ambassador to Mexico Christopher Landau said in a tweet in Spanish that "the safety of our fellow citizens is our top priority. I am closely following the situation in the mountains between Sonora and Chihuahua."
Landau, who earlier in the day said he was on his way to Sonora "for my first visit to the northeast of Mexico," did not share details of the incident. The U.S. State Department also said it was aware of the reports but had no further comment.
Claudia Pavlovich Arellano, the governor of Sonora, said on Twitter late Monday that "as a mother," she was filled with deep pain by "the cowardly acts in the mountains between Sonora and Chihuahua."
"I don't know what kind of monsters dare to hurt women and children," Pavlovich said.
Senator for Sonora, Lilly Téllez, said on Twitter “the massacre in Sonora cannot go unpunished.”
Manuel Añorve Baños, another Mexican senator, called what happened “a despicable, merciless and savage act” in a tweet, adding: “We demand justice.”