Iran says it has misgivings about the IAEA-brokered deal
The six major powers negotiating with Iran over its nuclear programme have said they are disappointed with Iran's response to an offer of a deal.
After talks in Brussels, the six said Iran had not responded positively to the offer, which would allow it to continue to develop a nuclear reactor.
The head of the UN's nuclear watchdog, Mohammed ElBaradei, had urged Iran to accept the deal by the end of the year.
But Iran rejected a key part of the deal, seeking further guarantees.
The BBC's Tehran correspondent Jon Leyne says that, while no-one wants to say that the Iranian nuclear talks have failed, this is the latest sign that they are not looking at all promising.
Friday's meeting involved the UN Security Council's permanent members - Britain, China, France, Russia and the United States - plus Germany.
NUCLEAR FUEL CYCLE
Mined uranium ore is purified and reconstituted into solid form known as yellowcake
Yellowcake is chemically processed and converted into Uranium Hexafluoride gas
Gas is fed through centrifuges, where its isotopes separate and process is repeated until uranium is enriched
Low-level enriched uranium is used for nuclear fuel
Highly enriched uranium can be used in nuclear weapons
The powers said in a statement: "Iran has not engaged in an intensified dialogue and in particular has not accepted... a new meeting before the end of October to discuss nuclear issues."
But they said it remained their objective to engage in dialogue with Iran.
A new meeting would be held to complete the powers' assessment of the situation and decide on the next steps to be taken, they added.
Some observers believe that Iran is stalling over the talks, but there are also concerns in the West that, following his disputed election, President Mahmoud Ahmadinejad simply does not have the power to push through a compromise on the nuclear issue even if he wants one.
The West fears Iran is trying to develop a nuclear weapons capacity. Iran insists its nuclear programme is for entirely peaceful purposes.
Mr ElBaradei - who is standing down as head of the International Atomic Energy Agency (IAEA) on 1 December - spoke earlier in Berlin, saying Iran had "a unique opportunity to move from sanctions and confrontation to the process of building... trust".
"I believe frankly the ball is very much in the Iranian court," he added. "I hope they will not miss this unique but fleeting opportunity."
On Wednesday, Iranian Foreign Minister Manouchehr Mottaki said his country had misgivings about the deal brokered by the IAEA.
It envisages Iran sending about 70% of its low-enriched uranium to Russia and France, where it would be processed into fuel rods for a research reactor in Tehran.
HAVE YOUR SAY
The best solution is for a progressive energy agreement
Gary Hay, Aberdeen/Chiba, Japan
Mr Mottaki suggested Iran would instead agree to exchange its uranium for an equivalent amount of nuclear fuel, but only on its own territory.
Tehran wanted to guarantee it would receive fuel it had contracted for, he said.
On Thursday US President Barack Obama said Washington and its partners would discuss "a package of potential steps" they could take if Iran snubbed a uranium enrichment deal.
Mr Obama said Iran needed to get a "clear message" that, if it failed to take advantage of such opportunities, it was "making itself less secure".
But Russia has said there is still "every chance" of reaching a deal with Iran on enrichment, and denied that it had been discussing further sanctions with Washington.
During Mr Obama's recent visit to China he received no assurances that Beijing would support new sanctions against Iran at the UN Security Council.
France and the UK want Iran to accept the deal.
The UN Security Council has called on Iran to stop uranium enrichment and has approved three rounds of sanctions so far - covering trade in nuclear material, as well as financial and travel restrictions.