Javier Solana, the European Union foreign policy chief, met Ali Larijani, Iran's nuclear negotiator, for more than five hours in Berlin on Wednesday for talks aimed at resolving the dispute over Iran's nuclear programme.
"The only thing I can say is that talks were very intense," said Christina Gallach, Solana's spokeswoman, as the two delegations left the Berlin meeting, adding that Solana and Larijani would reconvene in the morning.
The United States, Britain, France, Germany, Russia and China have offered Tehran economic and political incentives if it suspends uranium enrichment.
French officials said Larijani offered to consider a temporary enrichment suspension at a meeting with Solana two weeks ago.
Condoleezza Rice, the US secretary of state, spoke briefly with Solana immediately before his meeting with Larijani.
Rice played down prospects of a breakthrough.
She said: "Obviously, if we can come out of this with an Iranian decision to suspend its enrichment and reprocessing activities, completely and verifiably, then we would be on course for negotiations and that is the course we would all like to pursue.
"But I did wish Javier Solana luck and we are all awaiting the outcome of his discussion."
If Tehran does not suspend enrichment, the United States and the "EU3" - France, Germany and Britain - have agreed to ask the UN Security Council to impose sanctions on Iran. China and Russia oppose sanctions and would prefer to reopen negotiations.
A European diplomat confirmed a report by German magazine Der Spiegel, which said the EU3 would be willing to begin preliminary talks with Iran even if it does not suspend enrichment first.
Washington would not join in until a full suspension was in place.
"The idea would be to get Iran back to the negotiating table," the diplomat told Reuters on condition of anonymity.