Top diplomats from six key nations are meeting in London to discuss further moves to make Iran comply with demands to end its nuclear programme, BBC reports.
The talks come after the UN nuclear watchdog confirmed Iran had ignored a deadline to suspend nuclear activities.
The five permanent UN Security Council members and Germany will seek consensus on how to put more pressure on Tehran.
But on Sunday President Mahmoud Ahmadinejad said Iran would not go back on its nuclear programme.
Iran denies Western claims it is secretly trying to build nuclear arms, saying its nuclear programme is for peaceful, energy-producing purposes.
'Out of control'
The country's nuclear development was "a train on a one-way track with no room for stopping, reverse gear or braking," Mr Ahmadinejad said.
But the president's comments were later criticised by reformist newspapers which said the metaphor was inappropriate because it suggested the nuclear programme was out of control.
Correspondents say the coverage is the latest sign of growing criticism of President Ahmadinejad and what some call his confrontational manner with the West in pursuing Iran's nuclear programme.
Last week a radical reformist group, the Islamic Revolutionary Mujahadin Organisation, became the first political party to criticise the nuclear programme, saying it endangered the nation's security and interests.
Travel ban
Monday's meeting of diplomats from the US, Russia, China, France, the UK plus Germany will discuss how to make Iran meet UN demands to halt its nuclear enrichment activities.
The Security Council imposed sanctions on Iran in December, setting a 60-day deadline for it to stop enriching uranium.
But a report last week by the International Atomic Energy Agency (IAEA) said that Iran was instead expanding its enrichment programme.
Enriched uranium is used as fuel for nuclear reactors, but highly-enriched uranium can be used to make nuclear bombs.
The delegates will discuss new steps that could be taken to force Iran into line.
These, says the BBC's Jonathan Marcus, could include travel bans on named individuals associated with Iran's nuclear and missile programmes.
The US is also eager to discuss ways in which bilateral pressure can be applied on Tehran, with issues such as European export credits for business with Iran and arms sales from Russia on the agenda.
But, our correspondent says, the meeting is only the first step in what looks set to be an incremental process aimed at getting the Iranians back to the negotiating table.
On Sunday, Secretary of State Condoleezza Rice said the US would hold direct talks with Iran if it suspended uranium enrichment.
But a day earlier Vice-President Dick Cheney renewed a warning that the use of force could be an option if Iran continued to defy the West.
His remarks came as the investigative journalist Seymour Hersh reported in the New Yorker magazine that a special planning group had been set up in the US Joint Chiefs of Staff to coordinate bombing raids against Iran within 24 hours of a presidential order for military action.
Pentagon spokesman Bryan Whitman told the Associated Press news agency he knew of no such group and denied that the US was planning war with Iran.
Any suggestion of this was "wrong, misleading and mischievous", he said.
(BBC News, 26/02/2007)