Nuclear talks between Iran and the US have reached an impasse over Iran’s right to produce and stockpile low-enriched uranium. America first signalled that it was open to some enrichment before insisting that Iran must relinquish that right.

Iran’s supreme leader, Ayatollah Ali Khamenei, said on Wednesday that abandoning uranium enrichment was “100 percent” against Tehran’s interests, effectively rejecting a key U.S. demand in weeks of tense negotiations over Iran’s nuclear program.

The outline of the U.S. offer to Iran in their high-stakes negotiations over Tehran’s nuclear program is starting to become clearer.

The U.S. has started new talks with Iran, aiming to impose fresh nuclear restrictions on Tehran. For any deal to succeed, though, those IAEA blind spots will need to be closed, according to more than a dozen people familiar with Iran's atomic activities, including officials, diplomats and analysts.