US President Donald Trump has signed an executive order to keep immigrant families together who have been detained at the US-Mexico border.

Delivering his remarks at the 75th Anniversary Celebration of National Federation of Independent Businesses Trump said, "We're signing an executive order. I consider it to be a very important executive order. It's about keeping families together, while at the same time being sure we have a very powerful, very strong border".

Trump reversed his own policy amid heavy pressure from his fellow Republicans, Democrats and the international community, over the separation of undocumented parents and children.

Reportedly, nearly 2,000 children had been taken away from their parents in a six-week period in April and May under the new Trump administration policy. Mexico's foreign minister has termed the US policy "cruel and inhuman".

According to the order, most families would be kept together under the Department of Homeland Security, except in cases where an adult may pose a threat to a child.