"The secretary general has written to the governor of Oklahoma, Mary Fallin, to express his solidarity and to offer the assistance of the United Nations, if requested, to help with the recovery efforts," said deputy spokesman Eduardo del Buey.
Ban "sends his deepest condolences to those who have lost loved ones and to everyone affected by the storm," he said.
The giant twister tore through the outskirts of Oklahoma City Monday afternoon, causing chaos as it plowed over homes, schools and other buildings in its path.