British and US diplomats are among those meeting in Geneva to put more pressure on Iran to halt its uranium enrichment.
Representatives from the UK, US, France, Germany, Russia and China met in a hotel on the shores of Lake Geneva with Saeed Jalili, Iran's chief nuclear negotiator.
They are said to have insisted Iran name a date for a UN inspections of the nuclear plant in Qom, and have offered to freeze sanctions if Iranian uranium enrichment comes to a halt.
But during the morning’s session, Mr Jalili is said to have been keen to move discussion away from any concrete decisions, and has stressed Iran’s right to pursue a peaceful nuclear programme.
Britain’s representative is Foreign Office political director Mark Lyall Grant.
The countries, named the E3+3 group, are also said to have offered economic aid and technological assistance in using nuclear power as energy, in return for a freeze on uranium enrichment, which was also rejected by the negotiator.
If talks fail, the countries are expected to start discussing possible sanctions against Iran.
Meanwhile, Iranian Foreign Minister Manouchehr Mottaki has been in Washington to inspect Iran's unofficial office in the capital, but has not met with any US officials.