US and Iranian officials emerged upbeat from a meeting on Iran's nuclear programme.
However, both sides also sounded a cautionary note, with the US saying there was more work to do and Iran insisting on quick sanctions relief.
"Needless to say, one meeting and a change in tone, which was welcome, doesn't answer those questions yet and there is a lot of work to be done," said US Secretary of State John Kerry.
He was speaking after holding bilateral talks with Iranian Foreign Minister Mohammad Javad Zarif.
Mr Zarif said the sanctions are counter-productive and have to be removed "as we move forward".
Their talks followed a meeting between Iran and major powers about Iran's nuclear programme, which the US and its allies suspect aims to develop nuclear weapons.
Iran denies this and said the programme is for purely peaceful and civilian uses.
British Foreign Secretary William Hague said the tone and spirit of the meeting between the six powers and Iran was "extremely good".
Mr Zarif, Mr Kerry and Mr Hague were joined in the meeting by their counterparts from France, Russia, China and Germany.
It took place on the sidelines of the UN General Assembly in New York.