The researchers at the International Institute for Strategic Studies said they based their conclusions on public sources of information, including visits to nuclear sites arranged by Iranian authorities.
"Nevertheless," the institute’s director, John Chipman, told reporters, "there remains a good deal that cannot be known for certain from the outside."
LONDON — A leading British research institute said Tuesday that Iran stands at least five years away from producing sufficient material for "a single nuclear weapon," and it could achieve this only if it chose to ignore international reaction and "throw caution to the wind."
The researchers at the International Institute for Strategic Studies said they based their conclusions on public sources of information, including visits to nuclear sites arranged by Iranian authorities.
"Nevertheless," the institute’s director, John Chipman, told reporters, "there remains a good deal that cannot be known for certain from the outside."
Chipman presented the report at a diplomatically delicate time. Iran angered Western negotiators by resuming limited uranium conversion at Isfahan on Aug. 8 after a suspension of nuclear activities agreed upon with the European Union last November. And on Sept. 19 the board of the U.N. nuclear watchdog agency will meet to consider the next step.
Western nations, including the United States, have threatened to refer Iran to the Security Council, where it could face an array of penalties over its nuclear policies.
The United States argues that Iran is using its program to further its ambitions to produce nuclear weapons, but Iran maintains the program has only peaceful purposes.
The new report broadly concurs with one completed in May by American intelligence agencies, which concluded that analysts did not expect Iran to build a nuclear weapon before the next decade.
The institute’s report suggests that Iran has two principal options to produce highly enriched weapons-grade uranium, one at a relatively small pilot centrifuge at Natanz and the other at a planned industrial-scale centrifuge there, which might take more than a decade to build.
"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," and then only if it overcame an array of technical difficulties, the report said.
By contrast, "if Tehran does not feel compelled to acquire nuclear weapons urgently or judges that the risk of breaking out with a marginal capacity is too great, it could wait until it completes the industrial-scale centrifuge plant at Natanz."
While that might take more than 10 years, it would make it easier "to pursue covert enrichment options," the report said.
It said Iran’s "ability to produce weapons-grade plutonium seems more distant."
The report described Iran’s chemical and biological weapons as "much more difficult to assess." In a section on missiles, it said Iran had deployed up to 72 short- and medium-range missiles and possibly 12 intermediate-range missiles capable of striking targets in Israel, Turkey and southern Russia.
Chipman said the liquid fuel technology for the missiles had come from North Korea.
"As far as is known, Iran’s missile forces are armed with conventional high-explosive warheads," he said, adding that Iran could probably build primitive chemical or biological warheads "if it chose to do so."
Describing the diplomatic calculations, Chipman said negotiators needed "to apply pressure and create inducements to persuade Iran not to develop a fuel-cycle capability that it could turn later into a weapons program."
"On the other hand, it will be important to apply international diplomacy in such a way that does not inspire Iran to abandon all restraint and seek a nuclear-weapons capability without regard to international repercussions," he said.
The EU nations have said possibly only one option remained : to refer the Iranian issue to the U.N. Security Council, which has the power to impose sanctions.
"The logic of our position is that the [negotiating] bracket that has opened has now closed. It would be logical for this to be reported to the Security Council," said a high-level diplomat from the EU, who spoke on condition of anonymity because of the sensitivity of the issue.
He said not even a generous proposal by the 25-nation EU to strengthen economic and political ties and provide aid would sway Tehran now.
The Russian Foreign Ministry has said it opposes referring Iran to the U.N. Security Council over its nuclear program. Security Council member China also opposes the move, and it could use its veto power to block any resolution to punish Iran.
