Iran is clearly moving closer to acquiring a nuclear weapons capability but military strikes to counter the program would have serious unintended consequences, the top US military officer said Sunday.

"I think the unintended consequence of a strike against Iran right now would be incredibly serious, as well as the unintended consequences of their achieving a weapon," Admiral Mike Mullen, the chairman of the Joint Chiefs of Staff said.

"That''s why this engagement, dialogue is so important," he said in an interview on ABC television, referring to President Barack Obama''s aim to engage Iran diplomatically.

Mullen said the United States would approach Iran "with all options on the table."

"So that would leave a pretty narrow space in which to achieve a successful dialogue and a succesful outcome, which from my perspective means they don''t end up with nuclear weapons," he said.

Mullen said he did not believe Iran''s claims that it is developing its nuclear capabilities for peaceful purposes, but he said the aim of diplomacy would be "to really bring out whether that is how the senior leaders feels."

"Certainly from what I''ve seen in recent years, Iran is on a path to develop nuclear weapons," he said.

"Most of us believe that it is one to three years (away from acquiring nuclear weapons), depending on assumptions about where they are right now. But they are moving closer clearly and they continue to do that," he said.