Six key world powers pledged to reconvene on Thursday to continue work on a new, tougher UN Security Council resolution on how to tackle Iran's defiant nuclear programme.
After meeting in London to begin work on the new resolution, representatives from Germany and the five permanent members of the Security Council -- the United States, Britain, France, China and Russia -- will reconvene Thursday to discuss the "sanctions resolution", the US state department said.
The International Atomic Energy Agency (IAEA), the UN's nuclear watchdog, confirmed last week that Iran had ignored the Security Council's deadline to stop enriching uranium and had expanded its nuclear programme.
"We had a productive first discussion of the next steps following the director general of the IAEA's confirmation that Iran has failed to comply with SCR (Security Council resolution) 1737," John Sawers, the senior British Foreign Office official chairing Monday's talks, said after they broke up.
Sawers said they began work on a new Security Council resolution, and were considering "how best to re-engage with Iran."
"We are all committed to seeking a negotiated solution."
US State Department spokesman Sean McCormack said the parties involved would be in touch again Thursday via telephone "to hammer out the elements of a UN sanctions resolution".
He said the parties still wanted Iran to negotiate, but added: "We are equally committed to sending the message to the Iranian government: should they choose not to proceed down that pathway, then there will be consequences."
The already tense backdrop to the meeting was fuelled Sunday when Iran sent its first rocket into space and hardline President Mahmoud Ahmadinejad likened uranium enrichment to "a train on a one-way track".
There were also fresh indications of disagreement between some Security Council permanent members going into the talks.
The US, France and Britain want the Security Council to impose fresh sanctions but Russia and China, which hold veto rights and have economic, energy and strategic interests in Iran, are reluctant to pile on the pressure.
Former UN weapons inspector Hans Blix, a key opponent of the 2003 US-led invasion of Iraq, on Monday warned that "humiliating" Iran over its uranium enrichment could spawn intransigence.
"Why did the Iraqis behave as they did in the 1990s (and) send away the UNSCOM inspectors and close the door to them?" he asked, referring to the UN Special Commission mandated to inspect Iraqi weapons of mass destruction after the 1991 Gulf War.
"One element was 'humiliation'," he said.
Britain, meanwhile, insisted that the international community remains united in seeking to persuade Tehran to back down, while US Secretary of State Condoleezza Rice again offered Sunday to hold negotiations with Iran if it suspends enrichment.
"We're leaving open the track of negotiations, because the best way to resolve this would be to have Iran come to the table," she added.
In response, Iran stressed Monday that it would consider talks but would not stop its nuclear programme as a precondition.
"If the United States presents a request for negotiations through the official channels and it appears these negotiations are positive and constructive and logical, we are ready to examine this request with a positive eye," chief negotiator Ali Larijani told the IRNA agency.
"Fixing preconditions means that you have already determined the result of negotiations in advance and it is for this reason that such policies have produced no result up to now."
The US, while insisting it has no military plans against Iran, is beefing up its naval firepower in the Gulf.
Two US aircraft carrier groups are now there -- the highest concentration since the 2003 invasion of Iraq.
The New Yorker magazine reported Sunday that it is stepping up covert operations in Iran in a new strategy that risks sparking an "open confrontation" and benefits Sunni radicals.
Tehran insists that its uranium enrichment programme is designed to fuel power stations for civilians.