The US military is preparing to send as many as 5,200 troops to the nation’s southern border ahead of a migrant caravan travelling towards the region.

The latest reports arrived as an estimated 800 troops were sent to the US-Mexico border Monday, the US Department of Defence said Monday afternoon. By the end of the week, the department confirmed nearly 5,200 active duty troops would be assisting along the border with daily operations.

Meanwhile, the number of migrants continuing their collective journey has decreased each day, as is typical with the 15-year tradition that normally ends with a much smaller number of asylum-seekers arriving to US ports of entry along the border.

Earlier this year around 2,000 National Guard troops to the region, where about 15,000 US customs officials oversee the processing of trade, migrants and pedestrian travel daily.

The migrant group planned to set out early Monday for Niltepec, 43 miles, (70 kilometres) to the northwest in Oaxaca state.

Several hundred migrants tried to cross the Suchiate River from Guatemala to Mexico en masse on Monday, but were met by ranks of Mexican federal police who blocked them from entering.

The standoff on the riverbank follow a more violent confrontation that occurred on the nearby bridge over the river the night before, when migrants tossed rocks and used sticks against Mexico police. One migrant was killed Sunday night by a head wound, but the cause was unclear.

The caravan still must travel just under 1,000 miles (1,600 kilometres) to reach the nearest US border crossing at McAllen, Texas. The trip could be twice as long if the 4,000 or so migrants head for the Tijuana-San Diego frontier, as another caravan did earlier this year. Only about 200 in that group made it to the border.

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Donald Trump tweeted on Monday, “Many Gang Members and some very bad people are mixed into the Caravan heading to our Southern Border. Please go back, you will not be admitted into the United States unless you go through the legal process.”

He added, “This is an invasion of our Country and our Military is waiting for you!”

Most of the migrants in the caravan appeared determined to reach the US, according to the Associated Press, despite an offer of refuge in Mexico.

Mexican President Enrique Pena Nieto launched a program Friday dubbed “You are home,” which promises shelter, medical attention, schooling and jobs to Central Americans who agree to stay in the southern Mexico states of Chiapas or Oaxaca, far from the US border.

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Mexico’s Interior Ministry said Saturday that temporary identity numbers had been issued to 111 migrants, which would allow them to stay and work in Mexico. The ministry said pregnant women, children and the elderly were among those who had joined the program and were now being attended at shelters.

The president has repeatedly vowed to stop the caravan before any of its migrants arrive to the country, tweeting, “The migrant ‘caravan’ that is openly defying our border shows how weak & ineffective U.S. immigration laws are.”

“The big Caravan of People from Honduras, now coming across Mexico and heading to our “Weak Laws” Border, had better be stopped before it gets there,” he wrote in an additional tweet. “Congress MUST ACT NOW!”

The Pentagon declined to immediately comment on the latest reports. The White House also did not immediately respond to enquiries.