It's beyond dispute Iran is developing nuclear weapons and lying about it, Prime Minister Stephen Harper told CBC News chief correspondent Peter Mansbridge on Monday.

In an exclusive interview, Harper says the evidence, some from the International Atomic Energy Agency, is overwhelming that Iran has a nuclear weapons program.

"I think there is absolutely no doubt they are lying. Absolutely no doubt," Harper said of Iran's claims its nuclear program is for peaceful purposes.

An IAEA report last fall said some of Iran's clandestine activities could be for no other reason than a nuclear weapons program.

"And that, I think, is just beyond dispute at this point," Harper said. "I think the only dispute is how far advanced it is."

Last November, following the IAEA report, Canada, the U.S. and the U.K. imposed new sanctions on Iran's banking and oil and gas industries.

Harper says it's scary to hear what the Iranian regime says.

"I’ve watched and listened to what the leadership in the Iranian regime says, and it frightens me.

"In my judgment, these are people who have a particular, you know, a fanatically religious worldview, and their statements imply to me no hesitation about using nuclear weapons if they see them achieving their religious or political purposes. And … I think that’s what makes this regime in Iran particularly dangerous."

Foreign Affairs Minister John Baird has referred to Iran several times as the world's greatest threat to peace and security.

Harper says there's a "growing consensus" among world leaders, at least privately, that Iran's regime is dangerous, but there's no agreement on how to handle it. He pointed to a comment by U.S. President Barack Obama that all options are on the table and said he and Obama have talked about "the full range of questions around these issues."

"While there’s, I think, a growing belief of a number of governments that my assessment is essentially correct, I think there’s still big uncertainty about what exactly to do.

"Trade sanctions are something that just about everybody agrees on at some level, and everybody is doing at some level, but beyond that, these are not easy questions for the world."