LA MORA, Mexico (Reuters) - An American man whose grandchildren were slain in a massacre in Mexico demanded justice on Thursday for other victims of the country’s drug war, as relatives gathered from across the United States for a funeral guarded by heavily armed military.

Kenneth Miller lost his daughter-in-law and four grandchildren, all dual citizens, in an ambush on Monday in the northern border state of Sonora that killed three mothers and six children.

The attack on members of breakaway Mormon communities who settled in Mexico decades ago prompted U.S. President Donald Trump to urge Mexico and the United States to “wage war” together on drug cartels.

Fighting back tears before the first of the funerals for victims, in the La Mora village in Sonora, Miller said the family hoped the tragedy would draw attention to the thousands of victims in Mexico, where violence has reached a record.

“This is happening because we are dual citizens,” Miller said, referring to the Mexican government’s support following the attack. “There are thousands in this country who have never received justice.”

Just outside La Mora, an officer wearing a black helmet and a face mask stood beside a machine gun mounted on a truck, while about 40 soldiers, some in tan camouflage uniforms, toted high-caliber rifles.

Relatives gathered from both sides of the U.S.-Mexico border, family members said, including states such as Arizona, Colorado, Idaho, Iowa, North Dakota and Utah.

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Military and police escorted convoys of SUVs and pickup trucks from the border at Douglas, Arizona, on the four-hour drive south, mostly along dirt roads.

At the burial for Dawna Ray Langford, 43, and her sons Trevor, 11, and Rogan, 2, relatives streamed into the La Mora cemetery with somber expressions, carrying flowers and clasping hands.

Pallbearers lowered into the ground three simple wooden coffins built by family members and adorned with white, red and orange flowers.

Dawna’s mother, Karen Woolley, who said she resides in Utah but once lived in Mexico, spoke through tears about the loss of her daughter, one of her seven children.

“I can still hear her talking, saying ‘Hi Mom, good morning!’ You know? She will truly be missed, missed, missed,” she said.

Many mourners sank their heads into their hands during the funeral, where floral displays spelled out “MOM” in white daisies and “LOVE” in crimson roses.

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The victims came from prominent families which live in a handful of Mormon settlements in the area that date back decades, including the LeBarons, Millers and Langfords.

The oldest communities date from the late 1800s, when upheaval over polygamy in the Utah-based Church of Jesus Christ of Latter-Day Saints led to their founding.

The LeBarons, who came to Mexico in the early 20th century, now say they have more than 5,000 members.

“We came prepared to sleep on the floor, in tents,” said Alex LeBaron, a former Mexican congressman. “Whatever is needed to support the families who died in this terrorist act.”

His cousin Rhonita Miller, 30, and her four children, including twins nearly 8 months old, died in the attack, their bodies reduced to ash when their car went up in flames.

Authorities and relatives say the killings appeared to be the work of the Juarez and the Sinaloa cartels, which battle for control of lucrative drug routes through the sparsely populated mountainous areas into the United States.

Mexico has unleashed its military against cartels since 2006, but failed to reduce violence. Instead, the campaign has led to more killings as criminal groups splinter and fight among themselves.