Donald Trump is sending more than 5,200 troops to the US-Mexico border as he warned a caravan of migrants walking towards it: "This is an invasion".
The US military said 800 soldiers were heading to Texas "right now" on Monday afternoon to help secure the border before the remaining troops join them later.
The soldiers are being deployed by the Pentagon as part of a mission dubbed Operation Faithful Patriot to "harden" the southern border, supporting the border control and about 2,000 National Guard forces who have already been sent there.
They will mainly come from major army bases from across the entire country, two US officials said on condition of anonymity.
It was previously thought 800 military troops would be sent to the border as the group of 3,000 people makes its way to the border – but is still hundreds of miles away in southern Mexico.
Active duty troops are rarely deployed within the US except for domestic emergencies such as hurricanes and floods.
2:46The caravan started in Honduras on 13 October with about 1,000 Hondurans and has picked up more people as it travelled through Guatemala into Mexico.
The migrants from Honduras, Guatemala and El Salvador say they are fleeing persecution, poverty and violence in their home countries.
They are determined to make it into the US despite Mr Trump's public protestations, which ramped up today as he tweeted: "This is an invasion of our Country and our Military is waiting for you!"
Without providing any evidence, he claimed that "many gang members and some very bad people are mixed into the Caravan".
The president is keen to use the caravan to maintain a focus on immigration in the lead-up to the midterm elections next week which will determine whether the Republicans maintain control of Congress..
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. This is an invasion of our Country and our Military is waiting for you!
— Donald J. Trump (@realDonaldTrump) October 29, 2018
He is weighing up additional border security measures, including blocking migrants in the caravan from seeking legal asylum and keeping them from entering the US.
"This will be the election of the caravans, the Kavanaughs, law and order, tax cuts, and you know what else? It's going to be the election of common sense," Mr Trump said at a rally in Illinois on Saturday night.
Many of the migrants say they want to seek asylum in the US.
Under international law the US has to hear asylum claims from migrants who say they fear violence in their home countries.
However, US Attorney General Jeff Sessions announced in June that victims of domestic abuse and gang violence would no longer qualify for asylum.
Only those who are fleeing from a serious fear of persecution can apply, he said, despite these people being considered refugees under international law.
The caravan crossed from Guatemala into Mexico about 10 days ago by wading across the Suchiate River or on makeshift rafts.
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Another smaller caravan of about 600 migrants is following them, however the Mexican navy has since begun patrolling the river and police are insisting migrants register before entering with travel documents that many do not have.
One migrant died on Sunday night from a head wound as migrants tossed rocks and used sticks against Mexican police on a bridge over the river.
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Sky News
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