Iran is still short of the maximum amount of enriched uranium it is allowed to have under its deal with major powers but it is on course to reach that limit at the weekend, the latest data from U.N. nuclear inspectors shows, diplomats say.

On Wednesday, the U.N. nuclear watchdog verified that Iran had roughly 200 kg of low-enriched uranium, below the deal's 202.8 kg limit, three diplomats who follow the agency's work said.

Two of the diplomats said Iran was producing at a rate of around 1 kg a day, suggesting it will not make good on its announcement that it would reach the limit on Thursday. It could, however, go over the line soon after a meeting with other signatories of the deal in Vienna on Friday that is aimed at saving the accord.

"They haven't reached the limit... It's more likely to be at the weekend if they do it," one diplomat said on condition of anonymity.

The 2015 deal, which lifted international sanctions against Iran in exchange for restrictions on its nuclear activities, is aimed at extending the time Iran would need to produce a nuclear bomb, if it chose to, to a year from roughly 2-3 months.

Washington pulled out of the deal last year and has imposed punishing economic sanctions against Tehran.

Iran has threatened to respond by setting aside some of the deal's restrictions, which could cause the deal to unravel, but it has called on European powers to do more to shield it from U.S. sanctions.