Iran may achieve by mid-2014 the “critical capability” to process its low-enriched uranium into fuel for a nuclear weapon without detection by international inspectors, according to a report by a research group.

Iran would reach this capability by acting on plans to install thousands of additional enrichment centrifuges at its Natanz and Fordow sites, according to David Albright, a former nuclear inspector, and Christina Walrond of the Washington-based Institute for Sciences and International Security.

Preventing Iran from achieving the capability to break out from nuclear safeguards will require international efforts to limit the number and type of centrifuges that the Islamic Republic builds, according to the report issued Tuesday.

“Although increasing the frequency and type of inspections at the enrichment plants is important, it is by no means sufficient to prevent Iran from achieving critical capability,” according to the analysts.

President Obama has said the United States will prevent Iran from acquiring nuclear weapons. The United States and other world powers are seeking an initial agreement halting Iran’s production of 20 percent enriched uranium — one processing step short of bomb grade — and removing the stockpile of such medium-enriched uranium so that it can’t be diverted for weapons.

The ISIS report focuses instead on Iran’s production of low-enriched uranium, usable in fuel for civilian power reactors, which could be further enriched to bomb grade given time and ­sufficient centrifuges.

Albright and Walrond cited scenarios in which current safeguard measures would be insufficient to detect quickly an Iranian decision to divert enough low-enriched uranium to make weapons-grade material for one or more nuclear weapons.

“Breakout times at critical capability would be so short that there simply would not be enough time to organize an international diplomatic or military response,” they wrote.

Iran says its nuclear program is for civilian purposes. U.S. intelligence agencies have assessed that Supreme Leader Ayatollah Ali Khamenei hasn’t made a decision to produce a bomb, though Iran is developing its capability to do so.

Iran operates enrichment facilities in Fordow, near the holy city of Qom, and Natanz, 130 miles southeast of Tehran, that are monitored by the International Atomic Energy Agency.

Iran says the 20 percent enriched uranium, which has been of the most immediate global concern, is being processed to provide fuel for a research reactor used to produce medical isotopes.

The ISIS report says monitoring alone is insufficient and that international negotiations should press for a halt to installation of additional centrifuges and set a cap on the total number and capabilities of Iran’s centrifuges.

The report also raises the possibility that Iran may be building another enrichment facility that it hasn’t declared to the international monitors and that would provide an alternative route to a breakout nuclear-weapons capability.

The major world powers have been following a two-track policy: encouraging Iran to engage in diplomatic negotiations, while imposing increasingly comprehensive sanctions against Iran’s energy and financial sectors.