President Barack Obama's top military adviser says Iran's objective is to obtain nuclear weapons _ and that threatens the region.
Adm. Mike Mullen says he's worried about Iran and what U.S. 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.
Mullen appeared on ABC television's "This Week."
