"Iran has done a lot and much more than its fair share to preserve the nuclear deal," Ambassador Majid Takht Ravanchi told a council meeting.

"Iran alone cannot, shall not and will not take all of the burdens anymore to preserve the JCPOA," he said, referring to the Joint Comprehensive Plan of Action as the deal is formally known.

Iran has said that as of June 27, it will have more than the 300 kilos (660 pounds) of enriched uranium that it was allowed to have under the deal, the result of 12 years of tough diplomatic negotiations.

That move has raised alarm among the other signatories -- Britain, France, Germany, Russia and China -- which have urged Iran to stick to its commitments.

But the US ambassador argued that the US exit from the nuclear deal and the re-imposition of sanctions have rendered the JCPOA "almost fully ineffective."

Ravanchi insisted that the other signatories, namely Britain, France and Germany, must find a way to compensate Iran.

Iran's decision to scrap limits imposed by the nuclear deal on its uranium enrichment "may not help preserve" the landmark agreement, UN political chief Rosemary DiCarlo told the council.

Six European countries separately released a joint statement saying they were "extremely concerned" by Iran's latest move.

"We strongly urge Iran to continue to implement its commitments under JCPOA in full and to refrain from escalatory steps," said the statement from Britain, France, Germany, Poland, Belgium and Estonia.

Under the 2015 deal, Iran pledged to reduce its nuclear capacities for several years and allow in inspectors in exchange for sanctions relief.