For years, Iran has insisted that there are only peaceful, civilian purposes behind its nuclear program.

Those exhortations, however, did nothing to dim speculation outside the Middle Eastern country that there was a lot more going on at sites buried deep in the Iranian mountains — and it had nothing to do with peace or power generation.

A United Nations watchdog has put a much finer point on the whole matter, saying that Tehran is, indeed, on the brink of developing a nuclear warhead.

'I think the accumulation of evidence has been overwhelming.'— Aurel Braun, political science professor

The report from the UN International Atomic Energy Agency (IAEA) is the strongest signal yet that Iran wants to develop a nuclear arsenal.

"We must appreciate this is coming from an organization that in the past has bent over backwards to provide excuses for Iran," says Aurel Braun, a political science professor at the University of Toronto.

"This is not an organization that is anti-Iran. This is not an organization that is a tool of the U.S. This is not an organization that has a track record of making harsh statements about Iran or holding Iran to account."

So, something changed.

"I think the accumulation of evidence has been overwhelming," says Braun.

No choice

"The IAEA did not have a choice; they were not eager to do this," said Braun. "I think the malfeasance on the part of the Iranian regime reached the point that even the most objective, if you want to put it in a positive light, or the most sympathetic, if you want to put it another light, organization had no choice but to issue this assessment."

While the IAEA report talks about everything from clandestine procurement of equipment and detonator development to computer modelling of the core of a nuclear warhead, it's still hard to know exactly what is going on inside the Iranian nuclear program.

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Iranian students hold up their hands as a sign of unity as they form a human chain around the Uranium Conversion Facility in Isfahan to show their support for their country's nuclear program on Nov. 15, 2011. (Morteza Nikoubazl/Reuters)

"Think of it a bit like a mosaic where we're missing a bunch of the pieces, but we think we've got an idea of how the picture is coming together," says Christian Leuprecht, an international security expert and associate professor in the department of political studies at Queen's University in Kingston, Ont.

"And the picture for nuclear weapons looks like this: you need three elements to build a nuclear weapon. You need to be able to build the bomb, you need to be able build the trigger device and you need to have the delivery vehicle.

"So, we know the Iranians have the delivery vehicle, because, you'll recall, they've … sent a number of their short- and medium-range rockets up in the air to boast about those."

It also looks like they have, or are close to having, all the materials needed to build a weapon.

"The hardest thing is the trigger device, because you have to trigger a nuclear bomb in a chain reaction in a particular way, and this actually is quite difficult to do," said Leuprecht, adding that it appears that Iran has set off chain reactions.

"The concern is they now have all three of those pieces. Now, they still have to be able to put them together, and this is also not all that easy to do, but it would appear the Iranians are getting closer to where they're looking to be."

Link to the West

The Iranian nuclear program had its beginnings in the 1950s, and its start had a strong link to the West.

'We're somewhat at fault here for having instigated this … because we got them going on the nuclear path to begin with.'— Christian Leuprecht, security expert

Under the Atoms for Peace Program launched in the 1950s, the U.S. provided Iran with a nuclear reactor "for the civilian and peaceful use of nuclear energy," said Leuprecht, who is also an associate professor in the department of politics and economics at the Royal Military College of Canada in Kingston.

"So, in part, we're somewhat at fault here for having instigated this … because we got them going on the nuclear path to begin with."

In 1968, Iran signed the Nuclear Non-Proliferation Treaty and has said it has been living up to it.

The Iranian nuclear program went ahead with aid from the West for several years until "concern over Iranian intentions followed by the upheaval of the Islamic Revolution in 1979 effectively ended outside assistance," author Greg Bruno writes in an article posted on the Council on Foreign Relations website. In the 1990s, civilian nuclear programs got going again.

Leuprecht sees the latest IAEA report as offering more insight into what was going on over the years within the program.

"There's pretty overwhelming evidence that even though the Iranians said in 2003 that they were kind of scaling down the program and given that even U.S. intelligence in … 2006 told us that basically …  the program was hibernating, it turns out it doesn't appear to be the case," he said.

"It also suggests that there are probably more covert sites and more covert activity than we are aware of."

More covert activity

But potential covert activity isn't limited to efforts to advance the program.

The Stuxnet computer worm hobbled some centrifuges at Iran's main uranium facility in the city of Natanz last year. The virus was widely considered to be the work of Israel or the United States.

"That's the incident that's publicly known," said Leuprecht. "You can assume if that's what publically comes to light, that there's more activity than that in the works."

The best assessment Leuprecht has seen suggests Stuxnet set the Iranian program back nine months. But such actions are only stall tactics, he says.

The U.S. and its allies claim a nuclear-armed Iran could touch off a nuclear arms race among rival states, including Saudi Arabia, and directly threaten Israel. The West wants to use the IAEA report as leverage for possible tougher sanctions on Iran, but Israel and others have said military options have not been ruled out.

Ultimately, the question becomes how soon could Iran have a fully functional nuclear weapon — and whether it would use it.

"No one can answer with certainty," says Braun.

Sanctions have 'worked very well'

He sees a possible "peaceful way" out of the situation through the use of the harshest possible sanctions against Iran.

"But for this to work, you would need to have a really united international front," Braun said.

Russia and China haven't been very enthusiastic about such moves. Russia has already said it would not support new or tighter sanctions, despite the IAEA report.

"We do know the sanctions regime has worked very well over the last 10 years," said Leuprecht.

"We know that the Iranians [have] a massive problem borrowing on the international financial markets, which is partially why the economy is in shambles. Overall, the sanctions have caused great economic hardship."

Braun sees the potential for Canada to "play a very important role" in speaking to the international community and encouraging Russia and China that now is the time to institute effective sanctions against Iran.

"We can exercise leadership," he said. "I think we are a very respected member of the international community."

With files from The Associated Press