Adm. Mike Mullen told ABC's 'This Week' he's worried about Iran and what US intelligence agencies don't know about the Tehran government. The chairman of the Joint Chiefs of Staff says the United States and its allies must work to engage Iran's leaders.
Mullen says there's a narrow window in which to work to block Iran from achieving nuclear capabilities.
On Thursday Mullen said the consequences of Iran acquiring a nuclear weapon would be "calamitous" and major powers must act together to prevent it.
The remark came the day after Iran's president announced the country had tested a missile that analysts said could hit Israel and US bases in the Gulf, a major source of crude oil for the United States.
"I'm one who believes that Iran getting a nuclear weapon is calamitous for the region and for the world," Mullen told the US Senate Foreign Relations Committee.
"It then, in my view, generates neighbors who feel exposed, deficient and then develop or buy the capability themselves," he said, suggesting Iran's acquisition of a nuclear weapon likely would trigger a nuclear arms race in the Middle East.
"The downside, potentially, is absolutely disastrous."