Migrants who enter the U.S. illegally shouldn’t be surprised by recent reports of children being separated from their parents at the border — they should expect it, a top immigration official said Thursday.

Thomas Homan, the acting director of U.S. Immigration and Customs Enforcement, told the PBS NewsHour’s Judy Woodruff that migrants crossing the border “don’t understand” U.S. immigration laws.

“Apparently these people don’t understand what exactly is happening,” said Homan, who is retiring next month.

Homan said it’s “unfortunate, it’s sad” when children in the U.S. are separated from parents charged with crimes, including for entering the country illegally. But he noted there were logistical challenges in keeping families in those situations together. “A child can’t go to U.S. Marshals’ custody with the parents being charged with the crime of entering the country illegally,” he said.

Though federal officials have not provided specific figures on family separations at the border, more than 700 migrant children have been taken from adults claiming to be their parents since last October — including 100 children under age 4, according to a recent New York Times data review.

In the NewsHour interview, Homan urged eligible migrants to seek asylum instead of attempting to entry the country illegally.

“If they really are escaping fear and persecution, looking for relief in this country, why not come to a port of entry” and file for asylum, Homan said. In that scenario, he added, “you’re not taking your child across the river, you’re not taking them through a canyon, where that child could be hurt.”

Other highlights from the conversation: