US First Lady Melania Trump has spoken against a controversial administration policy that separates immigrant parents from their children at the Mexico border, media reports said.

"Mrs. Trump hates to see children separated from their families and hopes both sides of the aisle can finally come together to achieve successful immigration reform. She believes we need to be a country that follows all laws, but also a country that governs with heart," her spokeswoman Stephanie Grisham said in a statement on Sunday night.