US intelligence does not know whether Iran intends to develop nuclear weapons, but at a minimum is keeping open the option of developing them, the new US intelligence director said Thursday.

Retired admiral Dennis Blair said US intelligence assesses that Iran has not restarted nuclear weapons design and weaponization work that it halted in the fall of 2003.

"Although we do not know whether Iran currently intends to develop nuclear weapons, we assess Tehran at a minimum is keeping open the option to develop them," he said in an annual report to Congress.