US Attorney General Jeff Sessions warned during a visit to the border with Mexico on Monday that people who enter the US unlawfully with children will have them taken away.
"If you cross the border unlawfully, then we will prosecute you -- it's that simple. If you smuggle illegal aliens across our border, we will prosecute you," Sessions said.
"If you are smuggling a child, we will prosecute you. And that child will be separated from you, as required by law."
The trip marked the fourth recent visit by a high-ranking official from the administration of President Donald Trump to tout a zero-tolerance stance against illegal immigration.
The president was in Otay Mesa, a half-hour drive south of downtown San Diego, in March to survey prototypes of the border wall, a cornerstone of his presidential campaign.
The attorney general said the Department of Justice would send 18 immigration judges -- a 50 percent increase -- and 35 prosecutors to the Southwest region of the US, arguing that Americans had been "pleading" for tighter immigration enforcement for decades.
"The American people are right and just and decent to ask for this. They are right to want a safe, secure border and a government that knows who is here and who isn't," Sessions said.
"Donald Trump ran for office on that idea. I believe that is a big reason why he won. He is on fire about this. This entire government knows it."
His remarks were briefly interrupted by a lone protester shouting through a bullhorn, calling Sessions "evil" and asking if he had a soul.
The Democratic National Committee denounced Sessions's comments and the Trump administration's immigration policy as an "affront to our values as a nation."
"This administration is set on tearing families apart, detaining immigrants without justification, leaving US-born children without their parents and stoking fear in immigrant communities, all while siphoning off taxpayer dollars to fund a divisive and ineffective wall," a DNC statement said.
Sessions's visit came a week after a caravan of fewer than 200 migrants arrived at the US border in Tijuana following a month-long trek through Mexico.
The migrants have since begun the process of seeking asylum in the US.