VIENNA－Negotiations on reviving the 2015 Iran nuclear deal appear to be nearing a climax with talk of an imminent ministerial meeting as the United States said on Thursday that "a possible deal" is close but with some difficult issues yet to be resolved.

Negotiators meeting in Vienna have made "significant progress", US State Department deputy spokeswoman Jalina Porter told reporters, in comments that chime in with positive statements from other nations engaged in the process.

"We are close to a possible deal, but a number of difficult issues still remain unsolved," she said. "We will not have a deal unless we resolve quickly the remaining issues."

However, "if Iran shows seriousness, we can and should reach an understanding of mutual return to full implementation of the JCPOA within days", said Porter, referring to the Joint Comprehensive Plan of Action, the formal name for the nuclear accord.

Iran also said that the talks are in the "final critical steps".

"Nobody can say the deal is done, until all the outstanding remaining issues are resolved," Iranian Foreign Ministry spokesman Saeed Khatibzadeh tweeted.

Final critical steps

"Extra efforts needed. Everybody is now focused on the final critical steps," he said.

The 2015 deal secured sanctions relief for Iran in return for strict curbs on its nuclear program.

The agreement was struck by Iran with Germany, China, the United States, France, Britain and Russia.

The agreement unraveled when then US president Donald Trump withdrew his country from the pact in 2018. Israel had encouraged him to make the decision.

Iran's stockpile of enriched uranium has now reached more than 15 times the limit set out in the 2015 accord, the UN's nuclear watchdog said on Thursday.

A report by the International Atomic Energy Agency, or IAEA, showed that Iran's stock of uranium enriched up to 60 percent fissile purity had almost doubled to 33.2 kilograms.

Iran wants the IAEA investigation ended as part of an agreement but Western powers have argued that issue is beyond the scope of the 2015 deal, to which the IAEA is not a party.

IAEA Director-General Rafael Grossi will travel to Teheran on Saturday in the hope for an agreement on a "process" that would lead to the end of the investigation, potentially clearing the way for the wider agreement, diplomats said.

Agencies-Xinhua