Iranian officials ratcheted up pressure before a weekend deadline for European nations to come up with a solution for Iran to sell its oil abroad after the United States withdrew from a 2015 nuclear deal and reimposed devastating sanctions.
President Hassan Rouhani threatened on Wednesday to take additional steps and accelerate its nuclear activities if Europe fails to provide a solution by Friday.
"Iran's third step is of an extraordinarily significant nature," Rouhani said, without detailing what that would entail, adding a "decree will be announced today or tomorrow".
"I see that it's unlikely a conclusion will be reached with Europe today or tomorrow," he said, suggesting European powers have another two months to resume talks to save the landmark nuclear accord.
"They know what we want, and we know what they want."
A short time after Rouhani's statement, US officials announced new sanctions on Iran, this time targeting a shipping network it said was run by Iran's Revolutionary Guard to allegedly smuggle oil.
In two separate moves already, Iran reduced its commitments outlined in the deal and vowed further measures unless the European signatories of the pact did more to protect Tehran from the effects of the US "maximum pressure" sanctions campaign.
The nuclear deal - agreed on by Iran, Britain, China, France, Germany, Russia and the US - offered Tehran relief from many international sanctions in exchange for accepting curbs on its nuclear program.
Since Washington pulled out of the deal last year and reimposed sanctions, Iran has insisted it wants to save the pact but has demanded the remaining signatories - especially the Europeans - provide additional economic support.
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