At least nine members of a Mormon family, all U.S. citizens, were killed in northern Mexico in an apparent attack by drug cartels, prompting President Donald Trump to say America would help wipe traffickers “off the face of the earth.”

Mexican President Andres Manuel Lopez Obrador declined the offer Trump made on Twitter, where Trump suggested an army may be needed to fight the gangs. Lopez Obrador later spoke with Trump by phone to pledge justice would be done for the families, Foreign Minister Marcelo Ebrard said.

The exchange reflects diverging security policies between the U.S. and Mexico. AMLO, as the country’s president is known, has said he no longer wants violent confrontations with cartels and has given as an example the decision last month to release the son of kingpin Joaquin “El Chapo” Guzman to prevent attacks on citizens. Trump, who has often painted Mexico as a den of crime that threatens the U.S., is pushing for Mexico to take the opposite tack.

“This is the time for Mexico, with the help of the United States, to wage WAR on the drug cartels,” Trump tweeted after at least six children died in the attack.

The violence was the latest episode in a year when homicides are on track to reach a record despite AMLO’s promise to end the killings that have engulfed Mexico for more than a decade. By the end of September, 25,890 people had been murdered this year. While AMLO has created a national guard to protect citizens, he has said programs to fight poverty and nurture youth are the only long-term solutions.

Organized Crime

The LeBarons, the victims of Monday’s attack, were descendants of a group that fled the U.S. to avoid a ban on polygamy and started settling in Mexico in the late 19th century. They own land in Chihuahua state, a base from which they have publicly denounced organized crime in northern Mexico and even floated the idea of creating their own defense group to counter criminals.

The region where the family was killed is sparsely populated desert. Three women and 14 children were traveling from Sonora to neighboring Chihuahua when their cars were ambushed. The dead include 8-month-old twins. Six children survived, some after fleeing into the brush, and two were still unaccounted for, public security chief Alfonso Durazo said at a news conference.

Authorities couldn’t provide details about exactly what happened, but a video posted on Twitter by a member of the LeBaron family showed a charred, smoking vehicle in the middle of the road where the deceased were shot and burned alive.

Alex LeBaron, a relative, said in a radio interview that the motivation for the attack was a mystery.

“There was no explanation in any way,” he said. “There were no threats, no activism. It was a situation that happened during a caravan of women accompanied by their children. The criminals didn’t stop shooting.”

Trump lamented the killing of the “wonderful family and friends.” Some analysts said his expression of empathy was a calculated political move to force AMLO to crack down on criminals. Trump has used Mexican citizens as a foil since the earliest days of his candidacy, painting undocumented immigrants as an invasion of rapists and drug dealers.

“Trump’s tweets were clearly a veiled warning,” said Alejandro Schtulmann, who heads Mexico City-based risk consultant Empra. “In my opinion it won’t be a showdown but rather increased pressure from the U.S. and ultimately acquiescence from Lopez Obrador.”

But whatever Trump’s stance, the crisis of violence is real.

AMLO’s “government has neglected to address the growing epidemic of more specific and related crimes that are affecting a vast number of Mexicans,” Gladys McCormick, an associate history professor at Syracuse University in New York, said in an email.

The attack on the LeBaron family comes on the heels of other violent episodes in recent weeks, including the failed raid in Culiacan to capture Ovidio Guzman, the drug kingpin’s son. After security forces arrested him, gunmen terrorized the city with heavy weaponry until Guzman was freed.

Read more: Mexico’s AMLO lashes out at media after failed Culiacan raid

Lopez Obrador has said he is not changing his security strategy and refuses to counter violence with more violence.