Javier Solana and Tehran envoy Saeed Jalili made no comment ahead of the talks, which came hours before the Friday deadline after which Solana will report to major world powers on progress after almost 18 months of contacts.
But as the two men shook hands, an Iranian delegation member sought to put a positive spin on the meeting. "We are optimistic...We are going to present new ideas to Solana," he told AFP.
Solana's spokeswoman said the E.U.'s top diplomat had an open mind.
"He's here to listen to Mr Jalili and what Iranians put on the table," said Cristina Gallach, adding that the two sides were expected to issue a statement after the talks.
U.S. critics say Iran is continuing a long-standing strategy of diplomatic brinksmanship, offering last-minute compromises to delay further sanctions while pressing ahead with its nuclear plans.
While Iran says it was presenting new ideas to Solana, on the eve of the talks President Mahmoud Ahmadinejad remained defiant against international pressure for Tehran to suspend sensitive nuclear activities.
Iran insists that its nuclear programme is for civilian purposes, but its past obstruction of the U.N.'s atomic watchdog has fuelled fears Tehran is trying to covertly develop the bomb; a charge it firmly denies.
Tehran is under two sets of U.N. Security Council sanctions, as well as unilateral U.S. sanctions, for refusing to suspend uranium enrichment, which can fuel a nuclear reactor or, at highly refined levels, be used to build an atomic weapon.
Solana has been trying to create the conditions for broader negotiations in which Tehran would halt nuclear enrichment in exchange for a package of political, economic and trade incentives.
"What we are waiting for (from the talks) is, once again, to create the appropriate framework for the formal negotiations to begin," his spokeswoman said earlier this week.
Critics say Tehran has played off the five permanent security council members plus Germany - the six powers involved in the dossier - counting on China and Russia to block further sanctions demanded by the U.S.
Experts say prospects for defusing the West's nuclear standoff with Iran appear increasingly thin.
"I fear we might be on a path that might bring us to war. Diplomacy has not worked," said Mark Fitzpatrick of the International Institute for Strategic Studies (IISS) thinktank in London
"It is very clear that Iran is trying to acquire a nuclear weapons capability...Most of the world agrees that it is unacceptable," added the former U..S. State Department official.