Barack Obama has described the damage wreaked by last week's Oklahoma tornado as hard to comprehend when he saw the extent of the damage at first hand.

The US President stood for the first time in the midst of the destruction caused by the 17-mile long corridor of wind that flattened homes and schools in Moore, killing 24 people.

He pledged federal aid as he told residents: "Obviously, the damage here is pretty hard to comprehend."

He was speaking as he stood in a block where piles of boards, bricks and cinder blocks that used to be buildings and houses lined the side of the street.

"Whenever I come to an area that has been devastated by some natural disaster like this, I want to make sure that everyone understands that I am speaking on behalf of the entire country," said Mr Obama

"Everywhere, fellow Americans are praying with you, they're thinking about you and they want to help. And I'm just a messenger here letting you know that you are not alone."

Cars with dented bodywork and smashed windows lay under debris or twisted on their sides.

Rising above the wasteland were at least three American flags that had been attached to the rubble.

Caleb Sloan, 24, who lost his home, said Mr Obama's words gave him hope help would be forthcoming.

"He has no choice but to live by his word," Mr Sloan said. "I hope and pray and think he will keep his promises."