When we last left the Iranian WMD saga, it turned out that U.S. and U.N. intelligence were downgrading the likelihood of Iran developing nuclear weapons anytime soon.

In this week's installment, the International Institute for Strategic Studies (IISS) weighs in. Reuters provides the summary:

Iran, threatened with referral to the U.N. Security Council over its atomic ambitions, could develop bomb-making capability in as little as five years but a 15-year timeframe is more likely, a think tank said on Tuesday....

"If Iran threw caution to the wind and sought a nuclear weapon capability as quickly as possible, without regard for international reaction, it might be able to produce enough highly enriched uranium for a single nuclear weapon by the end of this decade," said John Chipman, director of London's International Institute for Strategic Studies.

He said technical problems could prolong the process and that given international pressure, the Islamic state was more likely to try to accumulate the capability over 10 to 15 years.

The evaluation by the influential think tank comes two weeks before the U.N. atomic watchdog (IAEA) will discuss whether to send Iran to the Security Council, possibly prompting sanctions.

The assessment is in line with British estimates, although U.S. intelligence reports have been more conservative, with a study last month putting the date for a bomb at 2015.

"Our assessment is technical," Gary Samore, editor of the IISS report, told reporters.

"The most interesting discussion is about political calculations and how Iran weighs the risks and benefits of acquiring nuclear weapons capability."

Samore said Iran appeared to be less worried about possible U.S. military action than two years ago, partly due to what he described as "the mess" in Iraq.

Click here to read Chipman's press release.