"I hope we will have good news to communicate to you … but I cannot guarantee success," Solana told reporters at a conference in Berlin.
In June, Solana presented Tehran with a package of economic and other incentives proposed by world powers to coax it to halt sensitive nuclear work the West fears is aimed at making bombs, a charge Iran denies.
Iran has offered its own package to resolve the dispute.
It has repeatedly refused to suspend its uranium enrichment activities, as demanded by six world powers before formal negotiations can begin on the offer.
Western diplomats say the powers — the United States, Britain, France, Germany, Russia and China — have conditionally offered to hold preliminary talks ahead of formal discussions.
Even for preliminary talks, the big powers say Tehran must freeze any expansion of its nuclear programme in return for the U.N. Security Council halting further sanctions measures.
(Reporting by Kerstin Gehmlich; Editing by Giles Elgood)
