The former United States First Lady Laura Bush has criticized a recent controversial policy that splits up families who illegally enter the country at the Mexican border.

Writing in the Washington Post newspaper, she describes the separation of children from their parents as cruel, immoral and heart-breaking.

Her comments follow growing controversy over President Donald Trump's "zero-tolerance" immigration policy.

Earlier Melania Trump made a rare statement expressing concern.

Mrs Trump "hates to see children separated from their families", her spokeswoman said.

She repeated her husband's call for "both sides" to work on immigration reform as a solution. However, fact-checkers point out that the policy was introduced by Mr Trump's attorney general and does not require congressional action to be stopped.

In a recent six-week period there were nearly 2,000 family separations following a crackdown on illegal border crossings.

Adults who try to cross the border outside of official entry points - many planning to seek asylum - are placed in custody and face criminal prosecution for illegal entry.

As a result, hundreds of children and babies are now being housed in detention centres, including warehouses and converted supermarkets, and kept away from their parents