PIEDRAS NEGRAS, Mexico -- Tensions began to rise before dawn as some 2,000 migrants being housed in a shelter in this border city woke up to a massive show of force gathering outside.

Just beyond a chain-linked fence topped with barbed wire, hundreds of Mexican federal, state and local law enforcement officers – clad in riot gear and armed with automatic weapons – stood vigilantly.

Military police soldiers marched in formation in the street behind them.

“Why are they there? We are not criminals,” shouted one migrant inside the fenced-in area.

Migrants are housed inside a warehouse, provided with food, blankets and healthcare but have not been allowed to come and go at will. Mexican officials said the tough stance was needed to ensure their safety.

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“It’s not that we’re trying to keep free people. They have to have migrant visas to be in our country and our city and trying to work together to handle this situation as best as we can,” said Piedras Negras Mayor Claudio Bres. “Instead of California, Arizona and New Mexico that all have all land territory, this is a river that in winter is very dangerous for people who don’t know how to swim and we’re not going to put them through that situation.”

Piedras Negras’ robust response comes as the U.S. promised to take “all steps” to make sure the “lawless caravan” doesn’t illegally enter the country.

“Illegal entry will not be tolerated and we stand ready to prevent it,” said a statement by Department of Homeland Security Secretary Kirstjen M. Nielsen. “DHS will do everything in its power – with the assistance of federal and state partners - to hold smugglers and traffickers accountable, enforce our laws, and keep American communities safe.”

The shelter is just few miles from the port of entry in Eagle Pass, Texas.

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The border itself is mostly separated by the Rio Grande with little or no wall or fencing in many places along the river, which makes it easier to cross in shallower spots.

Border Patrol officials said apprehensions of family units in this Del Rio sector are up 300 percent and water rescues are five times what they were this time last year.

This containment coupled with the show of force is quickly leading to restlessness among the migrants who have not experienced treatment like this since their journey began in Honduras 21 days ago.

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And it may get worse for those whose end goal was to illegally cross into America.

Governor Miguel Riquelme of the State of Coahuila told Fox News that anyone who has not accepted temporary asylum in Mexico will be deported.

“In coordination with the federal government, the immigration institute will come and work through all the papers and those that don’t have the right to be here, will be returned immediately to their place of origin,” he said.