"There is always progress in these talks, but insufficient," said Javier Solana.
The international community was still waiting for Iran's response to a proposed package of incentives for Tehran to give up its nuclear programme, he added.
"It was a constructive meeting, but still we didn't get the answer to our questions," said Solana.
The international community had proposed that "we refrain from Security Council resolutions and for Iran to refrain from nuclear activity including the installations of new centrifuges" for processing uranium.
"We are looking forward to an answer from Iran in this question… in a couple of weeks."
Russia's deputy foreign minister Sergei Kisliak was quoted by the Ria-Novosti news agency as saying that he expected a response from Iran in two weeks.
Iranian, European and US officials, including US State Department official William Burns, attended the talks in Geneva's historic Town Hall as part of a bid to resolve a long-running dispute over Tehran's nuclear programme.
In Washington, US State Department spokesman Sean McCormack said Burns delivered a "clear simple message" that the United States backed the incentives package and would only engage in negotiations with Iran when it halts uranium enrichment.
"We hope the Iranian people understand that their leaders need to make a choice between cooperation, which would bring benefits to all, and confrontation, which can only lead to further isolation," he said in a statement.
World powers have offered to start pre-negotiations during which Tehran would add no more uranium-enriching centrifuges and in return face no further sanctions — the so-called "freeze-freeze" approach.
Solana said that no fixed date had been set for this meeting, which could be held over the telephone and might only feature deputy officials rather than another high-level encounter.
Iran's top nuclear negotiator Saeed Jalili described the talks as "constructive and progressing," in comments to reporters afterwards.
He added that "on the manner of continuing the negotiations we have understood better our mutual positions.
"There are points in common and points that are not in common," Jalili said. "We have agreed to discuss this."
The Iranian representative compared the diplomatic process to weaving traditional Persian carpets: progress in cases "moves forward in millimetres," he said.
"It's a very precise work, in certain cases it's a very beautiful endeavour and hopefully the end result, the final product, would be beautiful to behold," Jalili said.
The attendance of Burns, the number three official at the State Department, marked a major policy shift by Washington, which has not had any diplomatic relations with Iran since 1980 following the Islamic Revolution.
McCormack said Burns did not meet or speak separately with any member of the Iranian delegation.
Western countries suspect Iran is secretly trying to develop a nuclear bomb and the United Nations has imposed several sets of sanctions against Tehran over its refusal to halt uranium enrichment.
Iran denies seeking nuclear weapons, insisting that its programme is designed to provide energy for its growing population for the time when its reserves of fossil fuels run out.
In London, British Foreign Secretary David Miliband hailed Burns's attendance as a strong signal of the West's determination to arrive at a negotiated solution.
"The message to Iran is simple: get serious about the real needs of your people, which are for a serious response to year on year diminution in their standard of living, and abandon the fiction that the world is pursuing a vendetta against you," he wrote in a blog on his ministry's website.
