MEXICO CITY — Members of Mexico’s newly created national guard are to be deployed this week to the country’s southern border, forming a force that will eventually reach 6,000 as part of the agreement with the United States that helped to stave off President Trump’s threat of tariffs.

But the national guard, which was proposed by President Andrés Manual López Obrador and ratified by Mexico’s Congress in March, was never presented to Mexicans as a tool of border security or migration enforcement. It has not received the training of a border patrol agency and has no formal connection to the country’s migration authority. It was intended instead to fill the security void left by Mexico’s ineffective and often corrupt local law enforcement agencies as violence here continues to climb.

Mexico recorded 8,493 homicides in the first three months of 2019, the most violent quarter here on record. That increase put pressure on López Obrador, who has long described himself as a pacifist. He announced the creation of the national guard this year and said the point of the force would be to ensure public safety.

“It will help us to face the problem of insecurity and violence by protecting citizens,” he said last month. “There will be peace, and there will be public security.”

The guard was to begin with 61,000 men and women, he said, drawn from Mexico’s military police, naval police and federal police. Human rights groups expressed concern about growing militarization and the track record of Mexico’s security forces. But the idea was mostly popular, and Mexico’s Senate approved it unanimously.

Then came Trump’s tariff threat and last week’s agreement on what Mexico would do to stem migration. Mexico’s foreign minister, Marcelo Ebrard, announced that 6,000 members of the national guard would be dispatched to the southern border beginning Monday, with a focus on 11 municipalities in southern Mexico.

It was a use of the national guard that most Mexicans had not expected. But according to Ebrard, the idea was not new.

“This was already planned,” he told reporters Monday morning. “We agreed to deploy them faster, that’s all.”

The reaction has not been entirely positive. A cartoon in Mexico’s Proceso newspaper on Monday showed Ebrard in an oversize U.S. Border Patrol uniform.

“Gift from Trump,” said the caption.

Guatemala is the single largest source of migrants to the United States. More than 211,000 Guatemalans were apprehended at the U.S. border in the eight months from October through May.

Mexico’s 540-mile border with Guatemala is mostly porous, with rivers, mountains and vast tracts of forest. Every day, traders and residents of both countries cross informally, often in rafts, just yards away from Mexican security officers. In some places, the border is marked only by carved white stones, hundreds of meters apart.

On Monday, many here were left trying to put the deployment in perspective. Alejandro Hope, a security analyst, wrote in El Universal that the number of national guardsmen was the equivalent of the entire state police force in several large Mexican states.

“So no, it is not a minor commitment to send 6,000 elements of the national guard to the southern border,” he wrote. “Maybe it's worth doing the expense to placate the monster that lives in the White House.”

Other Mexican analysts and former officials expressed concern that the national guard was not equipped to provide border security or to detain migrants.

The law that created the force granted members the ability to inspect migrants’ paperwork and assist the country’s immigration agency.

But it remained unclear exactly what role the force would play on the border. Many worried about the militarization of southern Mexico.

“It opens a big question, because the national guard isn’t trained for this type of work,” said Gustavo Mohar, a former senior migration and intelligence official. “It’s as though you sent the FBI or police of Texas.”

Mohar said deploying such a large force to the southern border meant redirecting the guardsmen away from fighting organized crime. 

“At the end of the day, the institutional capacity of Mexico is limited,” he said. “The demand to fight crime takes up everything — and we’re still short.” 

One approach the Mexican government has taken is to dispatch security agents — including those working with the country’s migration agency — to checkpoints north of the border. It is a similar approach to that of U.S. Border Patrol, which apprehends a large number of migrants at “interior” checkpoints.

Because a large number of migrants — especially those from Guatemala — are traveling by bus through Mexico, U.S. officials have suggested that Mexico should be able to easily identify and shutter smuggling operations.