Former White House senior advisor Stephen Miller on Thursday warned that the Biden administration is causing a "self-inflicted" public health crisis at the U.S.-Mexico Border after new policies have allowed potentially COVID-positive migrants into the country.

"He’s taken away from the Border Patrol the basic tools they need to keep this country safe," Miller said during an interview "Fox & Friends". "That’s why you’re seeing what you’re seeing."

Miller was referring to a 152% increase in expected illegal border crossings, including 700 children at the border without parents or adult supervision.

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Miller added that the implementation of a "tent-city" at the border and the reinstated catch-and-release policies force migrant children into contact with human traffickers and drug smugglers.

The former White House advisor also stated that under President Trump, immigrant minors were returned safely to their home countries with their families, instead of traveling and being held in some of the "worst [living] conditions imaginable."

The Biden administration announced this week that it opened a soft-sided facility for immigrants in Donna, Texas, as Republican lawmakers warned of a "rising crisis" at the border.

As previously reported by Fox News, the Department of Health and Human Services also plans to reactivate a temporary Influx Care Facility in Carrizo Springs, Texas, for the potential care of unaccompanied children detained at the country’s Southwest border.

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In a letter to the Biden administration, GOP lawmakers called for a briefing and warned of rising illegal immigration, noting an increase in the average daily flow of immigrants in the past month and a steady increase in immigration since the coronavirus pandemic began. By law, the government is required to provide aid to unaccompanied migrant minors below the age of 18 who are without a guardian in the U.S.

Fox News' Brittany De Lea contributed to this report.