Six world powers, represented by European Union foreign policy chief Catherine Ashton, have sought to persuade Iran to scale back its nuclear programme through intensifying economic sanctions and diplomacy.
The powers fear Iran is developing a bomb, but Tehran says its programme serves peaceful purposes only.
In the latest talks, Ashton and Iran's chief negotiator Saeed Jalili held a meeting in Istanbul that was described as "useful and constructive".
It was "an important opportunity to stress once again to Iran the urgent need to make progress," according to Ashton's spokesman.
Though three rounds of talks since April have made little progress, neither side wants to break off negotiations because of concerns that this could lead to a new war.
Israel, believed to be the only nuclear-armed state in the Middle East, sees a possible Iranian nuclear bomb as a threat to its existence and has said it may resort to military means if diplomacy and sanctions fail.
Any deals are likely to be struck only during political talks between Iran and the six powers - the United States, Russia and China, plus three EU nations: France, Germany and Britain.
Ashton "is planning to meet the Foreign Ministers of the EU 3 + 3 in the margins of the UNGA (United Nations General Assembly) ministerial week in New York in order to assess the situation and to discuss the way forward," her spokesman said in a statement.
Ashton is to leave for New York on Sunday and will likely stay until the following Friday, her spokesman said.
Pressure on Iran has been rising in recent weeks.
A meeting of EU foreign ministers in Cyprus earlier this month produced support from France, Britain and Germany for further sanctions on Iran. The EU has already banned oil imports from Iran and isolated its banking sector, while the United States ratcheted up sanctions over the summer to punish banks, insurers and shippers that help Tehran sell oil.
British Foreign Secretary William Hague said last week that EU members were drawing up the new sanctions with a view to discussing them in mid-October.
The International Atomic Energy Agency censured Iran last Thursday for defying international demands to curb uranium enrichment and failing to address mounting disquiet about its suspected research into atomic bombs.
At the core of the discussions are Iranian efforts to enrich uranium to 20 percent fissile purity, an advance that would bring it close to acquiring weapons-grade material.
World powers demanded during this year's talks that Tehran abandon such production, ship stockpiles out of the country and close an underground facility where high-grade enrichment takes place. Tehran has refused to meet the demands unless economic sanctions are lifted.