Iran may be able to make a nuclear weapon in as little as one or two years if it chose to do so, an influential think-tank said on Thursday.
The International Institute for Strategic Studies (IISS) said in a report that evidence showed "beyond reasonable doubt" that Iran was seeking the capability to produce nuclear weapons should its leaders decide to go down that route.
However, allegations that Iran had carried out prohibited chemical or biological weapons activities "cannot be determined from the available public information and may have been exaggerated," the IISS said in a 128-page report on "Iran's nuclear, chemical and biological capabilities".
Iran is locked in a standoff with the United States and other powers over its nuclear programme, which Tehran says is peaceful but the West suspects aims to develop a nuclear bomb.
The United Nations Security Council has imposed four rounds of sanctions on Iran over the programme. Estimates of when Iran might be able to produce a nuclear bomb are important because of speculation that Israel or the United States might launch military strikes to prevent it from doing so.
The London-based IISS said Iran's current stockpile of low-enriched uranium (LEU) would, if further enriched, be enough for one or two nuclear weapons.
If the 4,000 centrifuges that appeared to be working well at Iran's Natanz enrichment plant were used for weapons purposes, and they continued to perform at their maximum output to date, "a little over a year and seven months would be required for the first bomb's worth of HEU (highly enriched uranium)," it said.
This assumed Iran would use a four-stage production method developed by Pakistan and sold by Pakistani nuclear scientist A.Q. Khan on the black market, it said. Khan confessed to selling nuclear secrets to Iran, North Korea and Libya in 2004.
Producing HEU for subsequent bombs would be quicker than the first one -- taking a minimum of 32 weeks each, the report said.
In theory, a quicker method, called a batch enrichment process, could be used, allowing the first weapon's worth of HEU to be produced in six months and sufficient quantities to make subsequent bombs in four months.
However, this method had never been used in practice and it seemed unlikely Iran would choose it, the report said.
Whichever method was used, at least six more months would be required to convert the HEU from gas form into metal and fashion it into a weapon, the report said.
"The minimum timeline then for the first weapon is over two years under the Pakistan method and one year for the batch method," the report said. Developing a means to deliver a nuclear weapon -- a missile -- added to the timeline, it said.
The report chimes with comments made this week by British Defence Secretary Liam Fox who said Western powers should work on the assumption that Iran could have a nuclear weapon by next year.
The IISS said that for Iran to have a credible nuclear deterrent, one bomb would not be enough.
"Given the need for a replacement in case of bomb failure, as well as the presumed requirement for a second-strike capability and possibly for a test, it would seem foolhardy for a nation to go for broke, with the international reaction this would entail, before it could manufacture at least a handful of weapons," the report said.
That would multiply the amount of weapons-grade uranium and time that would be needed, it said. (Editing by Keith Weir)
© 2015 Thomson/Reuters. All rights reserved.