The meeting of the International Atomic Energy Agency (IAEA) was requested by the US after it was confirmed last week that Iran had exceeded the stockpile of enriched uranium permitted under the 2015 Joint Comprehensive Plan of Action (JCPOA).

The US Ambassador to International Organizations in Vienna Jackie Wolcott told the meeting that Iran was engaged in "nuclear extortion".

Iran has said it will disregard certain limits under the JCPOA as long as the remaining parties to the deal -- in particular the UK, France and Germany -- don't do more to mitigate the impact of crippling US sanctions re-imposed after President Donald Trump withdrew from the deal in May 2018.

"There is no way to read this as anything other than a crude and transparent attempt to extort payments from the international community," Wolcott said.

Her Iranian counterpart Kazem Gharib Abadi said it was a "sad irony that this meeting is convened with the request of the United States".

Gharib Abadi said the current impasse was the result of the Washington's "outlaw behaviour" and condemned what he called the "sadistic tendency" of the US to impose sanctions on Iran.

Russia's Ambassador to the IAEA Mikhail Ulyanov tweeted after the meeting that the US "was practically isolated on this issue".

He told the assembled diplomats it was an "oddity" that the meeting had been called by the US, "the country that declared the JCPOA to be a 'terrible deal'".

"In practice, it turns out that Washington is aware of the importance of the Plan (JCPOA)," he said.

A US administration official insisted that the Iranian and Russian position did not reflect the majority feeling among members.

The official did however confirm that the United States had discussed with the remaining three European parties to the JCPOA whether they would be prepared to call the IAEA meeting, before doing so itself.

In a joint statement to the meeting, Britain, France and Germany took a nuanced position, reflecting their continued diplomatic efforts to save the JCPOA.

They said that "our continued support (for the JCPOA) relies on Iran implementing its commitments in full".

However, the statement added: "We believe the issues at hand should be addressed by participants to the JCPOA, including through a meeting of the Joint Commission to be convened urgently".

Following the breach of the uranium stockpile limit, on Monday the IAEA also confirmed that Iran had breached the uranium enrichment limit, fixed at 3.67 percent in the JCPOA.

A diplomatic source said on Wednesday that the IAEA had confirmed Iran's assertion earlier this week that it was enriching to 4.53 percent, well below the 90 percent level experts say is needed to equip a nuclear weapon.