MEXICO CITY — Drug cartel gunmen ambushed three SUVs along a dirt road, slaughtering at least six children and three women — all of them U.S. citizens living in northern Mexico — in a grisly attack that left one vehicle a burned-out, bullet-riddled hulk, authorities said Tuesday.

The dead included 8-month-old twins. Eight children were found alive after escaping from the vehicles and hiding in the brush, but at least five had bullet wounds or other injuries and were taken to Phoenix for treatment.

Sen. Mitt Romney says he’s been briefed on the slaying of nine U.S. citizens in northern Mexico and calls it “a great tragedy” and something “really unthinkable.”

The Republican from Utah said Tuesday that the attacks were probably “associated with the business of the cartels” rather than a targeted attack on the U.S.-affiliated religious community.

He said he agrees with President Donald Trump that “Mexico has to really knuckle down and go after some of these cartels and stop this escalating level of violence.”

The victims are members of a faction that long ago broke away from The Church of Jesus Christ of Latter-day Saints and some have family ties in Utah.

Romney’s own father was born in a similar but different group in northern Mexico. He said he doesn’t know any of the people involved.

Utah Congressman Ben McAdams also released a statement on the tragic event.

“It’s outrageous that mothers and children cannot drive in the area without being gunned down by these violent criminals,” McAdams said in a press release. “I learned from my recent visit with Republicans and Democrats to border facilities in McAllen, Texas that the drug cartels operate with near impunity and are a threat to the safety of U.S. and Mexican citizens, to asylum-seekers from Central America, and to our border security.”

McAdams expressed his “deepest sympathies” for family and friends of the shooting victims.

Mexico’s foreign secretary says President Andrés Manuel López Obrador has phoned U.S. President Donald Trump to express condolences at the slaying of nine members of a religious community in northern Mexico, saying they were citizens of both nations.

Marcelo Ebrard says the Mexican leader expressed “thanks for the offer of help, if Mexico needs some sort of help.” And he said Trump “reiterated confidence” in Mexican authorities “to apply justice.”

The comments were carried in a video on the Reporte Indigo news website.

Earlier Tuesday, Trump tweeted an offer to help Mexico “wage WAR” against drug cartels suspect of committing the killing in a mountainous part of northern Mexico.

López Obrador expressed thanks to Trump during a later news conference, but demurred at Trump’s offer, saying “The worst thing you can have is war.”

The attackers apparently killed one woman, Christina Langford Johnson, after she jumped out of her vehicle and waved her hands to show she wasn’t a threat, according to an account published by family members and corroborated by prosecutors and a relative in a telephone interview.

Around the ambush scene, which stretched for miles, investigators found over 200 shell casings, mostly from assault rifles.

The attack took place Monday in a remote, mountainous area in northern Mexico where the Sinaloa cartel has been engaged in a turf war. The victims had set out to see relatives in Mexico; one woman was headed to the airport in Phoenix to meet her husband.

Mexican Security Secretary Alfonso Durazo said the gunmen may have mistaken the group’s large SUVs for those of rival gangs.

“There’s apparently a war right now,” a relative of the dead who did not want his name used for fear of reprisals said wearily. “It’s been going on for too long.”

While a drug-related violence has been raging for years in Mexico, cartel gunmen have become increasingly unconcerned about killing children as collateral damage. In August in Chihuahua state, gunmen fired 123 bullets at a man but also killed three girls, ages 4, 13 and 14.

The victims in Monday’s ambush lived in neighboring Sonora state, about 70 miles south of Douglas, Arizona, in the hamlet of La Mora, which was founded decades ago by an offshoot of The Church of Jesus Christ of Latter-day Saints.

A number of such American farming communities are clustered around the Chihuahua-Sonora border. Many members were born in Mexico and thus have dual citizenship. While some of the splinter groups were once polygamous, many no longer are.

All of the victims were apparently related to the extended LeBaron family in Chihuahua, whose members have run afoul of the drug traffickers over the years. Benjamin LeBaron, an anti-crime activist who founded neighborhood patrols against cartels, was killed in 2009.

State prosecutors said Johnson, the woman who waved her arms, was found 15 yards away from her Suburban van, shot to death. Her 7-month-old daughter, Faith Marie Johnson, was discovered uninjured in her car seat.

Kendra Miller, a relative, wrote that the baby’s car seat “seemed to be put on the floor, by her mother to try and protect her. ... She gave her life to try and save the rest.”

A short distance away, Dawna Ray Langford, 43, lay dead in the front seat of another Suburban, along with the bullet-riddled bodies of her sons, ages 11 and 2.

Some of the children who escaped had grisly wounds. One had been shot in the face, another in the foot. One girl suffered gunshot wounds to her back and foot.

Cowering in the brush, one boy hid the other children and then walked back to La Mora to get help. Another girl, who was initially listed as missing, walked off in another direction, despite her gunshot wounds, to get help.

A group of male relatives set out to try to rescue the youngsters but turned back when they heard gunfire ahead.

The relative who did not want his name used said in an interview that when they finally made it to the scene where the ambush started — about 11 miles from where the two other mothers were killed — they found a burned-out, shot-up Chevy Tahoe.

Inside, they saw the charred remains of Rhonita Miller, 30, her 10-year-old daughter, a son, 12, and 8-month-old twins. They were “burnt to a crisp,” the relative said.

The gunmen had riddled the vehicle with dozens of bullets and apparently hit the gas tank, causing it to explode. There was nothing the relatives could do but watch the still-smoldering vehicle.

“When we were there, the cartels from Sonora, there were probably 50 or 60 of them, armed to the teeth, about a mile on this side,” said the relative.

Trump tweeted that a “wonderful family” got “caught between two vicious drug cartels.”

He tweeted that the U.S. “stands ready, willing & able to get involved and do the job quickly and effectively,” adding, “The great new President of Mexico has made this a big issue, but the cartels have become so large and powerful that you sometimes need an army to defeat an army!”

But Mexico’s president said: “The worst thing you can have is war.”

It was the second failure in recent weeks for López Obrador’s “hugs not bullets” anti-crime strategy. Two weeks ago, Mexican forces seized a son of imprisoned drug lord Joaquin “El Chapo” Guzman but had to release him after cartel henchmen launched a furious counterattack in Culiacan, Sinaloa.

Prosecutors on Tuesday said a suspect was detained near Agua Prieta, but it was unclear whether the person had taken part in the ambush. The suspect had assault rifles and a .50-caliber sniper rifle and was holding two bound kidnap victims, authorities said.

The 2009 killing of Benjamin LeBaron marked a watershed in Mexico’s 2006-12 drug war. Gunmen tortured him in front of his family, then killed him and his brother-in-law.

But the 2009 killings — which sparked a further crackdown on cartels — also showed how much worse things have become: No children were killed back then.

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