US President Barack Obama has visited tornado-devastated Moore, Oklahoma, promising that the government will be behind them "every step of the way".

"I'm just a messenger here," Mr Obama said, adding "folks are behind you" across America.

He offered moral and monetary support in the wake of the tornado that killed 24 people last Monday.

The extraordinarily powerful twister that struck Moore was known as an EF5, ranking it at the top of the enhanced Fujita scale used to measure tornado strength.

Standing with Oklahoma Governor Mary Fallin and other state and federal officials, Mr Obama noted the substantial rebuilding job ahead and said "our hearts go out to you".

"This is a strong community with strong character," he said. "There's no doubt they will bounce back. But they need help."

The White House said the Federal Emergency Management Agency has already provided $57 million (€44m) in rebates and incentives to help build about 12,000 storm shelters in Oklahoma.

"These storm shelters can be the difference between life and death," presidential spokesman Josh Earnest told reporters accompanying Mr Obama to Oklahoma on Air Force One.

Among the tornado victims were ten children, including two sisters pulled by the strong winds out of their mother's grasp, an infant who died along with his mother trying to ride out the storm in a convenience store and seven students at Plaza Towers.

Many students were pulled from the rubble after the school was destroyed.