Talks between EU and Iranian officials in Brussels have ended without progress, a UK diplomat has said.
Western powers suspect Iran's nuclear ambitions are not peaceful
A UK diplomat said the EU3, the foreign ministers of the UK, Germany and France - had not heard anything new.
The Iranian official, Javad Vaeedi, cast the talks in a positive light and said he hoped the talks would continue.
The UN's nuclear watchdog, the IAEA, is meeting in Vienna on Thursday and could refer Iran to the UN Security Council for possible sanctions.
Diplomats from EU3 plus the US, Russia and China are meeting for dinner in London on Monday evening to try to agree a common stance ahead of the Vienna talks.
The talks in Brussels were requested by Tehran in the hope of averting moves towards referral.
"To be frank, we didn't detect anything new in their approach," said John Sawers, a senior British diplomat at the talks.
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Mr Vaaedi, deputy head of Iran's Supreme National Security Council, said: "As far as we are concerned, it has been a positive outcome."
At the talks in Vienna on Thursday, the International Atomic Energy Agency (IAEA) will consider EU and US arguments that Iran should be referred to the Security Council.
Washington and the EU have accused Iran of aiming to produce nuclear weapons, but Tehran insists its nuclear programme is for civilian energy use only.
Many Western powers and also Israel distrust Iran, partly because it had kept its nuclear research secret for 18 years before it was revealed in 2002.