Mexico has sent almost 15,000 soldiers and National Guard north to stem the flow of illegal immigration across the border into the US, the head of the country's army said on Monday.

Mexico has not traditionally used security forces to stop undocumented foreign citizens leaving the country for the US, and their actions at the border in recent days have been criticised.

The move came after the threat of tariffs on its exports by US President Donald Trump, who has made tightening border security a priority.

Responding to weekend reports of heavy-handed intervention by the military, Luis Cresencio Sandoval, the head of the Army, said soldiers were needed to back up migration officials.

And about 6,500 members of the security forces were sent to Mexico’s southern border area with Guatemala, Mr Sandoval said.

“If we left it completely in the hands of the National Institute of Migration it wouldn’t be possible,” he said. “That’s why we’re providing support. It’s a strategy being pursued on both borders.”

The National Guard, a force of soldiers, marines and federal police, is at the heart of Mexican President Andres Manuel Lopez Obrador’s plan to restore order in a country with record levels of violence.

The force is still taking shape, and due to be led by a retired general in the Security Ministry.

National Guard members on Friday were filmed detaining Cuban and Central American women trying to illegally cross from Ciudad Juarez, Mexico, into El Paso, Texas.

Former Mexican national security official Gustavo Mohar said the country’s forces had not been used this way before. He said the development was “sad.”

Mr Mohar blamed the change on the Mr Trump's threats to impose tariffs.

The National Guard should not be implementing migration policy, he said, while acknowledging that Mexican migration authorities were overwhelmed.

Mexico on June 7 agreed to reduce significantly the number of migrants reaching the US border within 45 days.

If that fails, Mr Lopez Obrador’s government said it would consider changing its laws to satisfy Mr Trump’s demand that Mexico become a buffer zone to stop migrants entering the US.

Most of the people caught on the US-Mexico border are from three Central American countries suffering from gang violence and poverty – Guatemala, Honduras and El Salvador.

Mr Trump has said he will impose initial tariffs of 5 per cent on all Mexican goods if the migrant flow is not curbed. The tariff could eventually rise as high as 25 per cent, he said.

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The National

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