Gulf tensions have intensified after Iran reacted to US threats by speeding up nuclear enrichment.
The EU had put up $15bn (€14bn) to bailout international diplomacy.
But hawkish US talk derailed the French-led initiative.
"From Friday (6 September), we will witness research and development on different centrifuges ... needed for enriching uranium in an accelerated way," Iranian president Hassan Rohani said on state TV on Wednesday.
"It is unlikely that we will reac...
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