The chairman of the Joint Chiefs of Staff said that Iran is clearly on a path to building nuclear weapons and that military options have been on military leaders' minds "for a significant period of time."

But Adm. Mike Mullen, in an interview to air this weekend on CNN's "Fareed Zakaria GPS," said that diplomacy remained the No. 1 strategy for reining in a nuclear program that Tehran claims is for peaceful energy purposes.

"I still think it's important we focus on the dialogue, we focus on the engagement, but also do it in a realistic way that looks at whether Iran is actually going to tell the truth, actually engage and actually do anything," Mullen said.

"They've got a history of gamesmanship that certainly doesn't include closing on significant steps to indicate to the international community that they're not doing this," he added.

Iran announced Saturday that its Bushehr nuclear plant, built by Russia, had begun operations and officials claimed it would begin contributing to the national energy grid "in a month or two."

"I don't believe it for a second," Mullen responded when asked whether Iran's nuclear program was for energy. "In fact, the information and intelligence that I've seen speak very specifically to the contrary."

Mullen and other leaders have cautioned that a military strike might delay the inevitable nuclear development but not halt it.

"Iran is still very much on a path to be able to develop nuclear weapons, including weaponizing them, putting them on a missile and being able to use them," Mullen said.