(CNN) Former first lady Laura Bush spoke out Sunday night about the separation of families on the US border, writing a harsh criticism of the current zero-tolerance immigration policy being enforced under the Trump administration.

Bush, whose opinion piece ran in The Washington Post, decries the separation of children from parents entering the United States illegally as "cruel" and "immoral."

It's a rare public admonishment of current administration policy from Bush, who has seldom weighed in on politics since her husband left office.

"I live in a border state. I appreciate the need to enforce and protect our international boundaries, but this zero-tolerance policy is cruel. It is immoral. And it breaks my heart," Bush writes.

"Our government should not be in the business of warehousing children in converted box stores or making plans to place them in tent cities in the desert outside of El Paso," she continues. "These images are eerily reminiscent of the Japanese American internment camps of World War II, now considered to have been one of the most shameful episodes in U.S. history."

Read More