Although this is less than the amount required to make a nuclear bomb — about 130 kilograms at the very least — there are still concerns that Iran could stockpile enough of this uranium and then quickly enrich it further in order to produce weapons-grade material.

There is also the concern that Ahmadinejad’s offer may be empty rhetoric. His domestic standing has weakened following his recent public rifts with Supreme Leader Ali Khamenei. But Ahmadinejad has repeated the offer often enough, and with confirmation from the foreign minister, that it must have the backing of the Iranian political elite, including Khamenei.

And recent statements by Fereydoon Abbasi, the head of Iran’s atomic energy agency, rebuffing the possibility that Iran might halt production of 20 percent-enriched uranium or agree to fuel swaps, should not be taken too seriously. Abbasi is often belligerent — perhaps the result of being targeted for assassination last year — and traditionally neither he nor his predecessors have been included in the Iranian government’s decision-making on nuclear issues. The reality is that Tehran needs nuclear fuel for its research reactor, and it needs it now.

For once, it is strategically expedient for the United States and its allies to take Ahmadinejad at his word. They should provide Iran with 50 kilograms of fuel, without any conditions.

As the failed experiences of 2009 and 2010 demonstrated, setting conditions would be a nonstarter. On the other hand, giving Iran the fuel unconditionally would remove Iran’s rationale for refining uranium to more than 3.5 percent.

The deal would increase Iran’s safeguarded stockpile of 20 percent-enriched uranium to 120 kilograms, an amount large enough to operate the Tehran Research Reactor for seven years at maximum capacity — and help the 850,000 Iranians who currently depend on the reactor’s radioactive isotopes for cancer treatment — but too small to produce even one nuclear bomb.

Such a move would be, above all, a humanitarian gesture, and it would buy Washington good will with the Iranian people and undermine the regime’s anti-American, nationalistic propaganda. But it would be a humanitarian gesture with strategic benefits: curtailing Iran’s enrichment activities and potentially cutting the Gordian knot that has stalled the West’s nuclear negotiations with Iran.