WASHINGTON (AP) - United States President Barack Obama said he is instructing his disaster response team to get tornado victims in the south-west state of Oklahoma everything they need "right away".

Mr Obama called the devastation that tore through the Oklahoma City suburbs "one of the most destructive tornados in history", even though he said the extent of the damage is still unknown.

Mr Obama spoke on Tuesday after a briefing on the latest developments from his disaster response team and as Federal Emergency Management Agency director Craig Fugate was heading to Oklahoma.

Mr Obama has declared a major disaster in Oklahoma, ordering federal aid to supplement state and local recovery efforts.

The President said there will be a long road of recovery ahead. But he said the victims will not travel alone, and will have the resources they need.