US Secretary of State John Kerry has said he had a "good meeting" with his Iranian counterpart and a senior European Union official over Iran's nuclear programme.
The talks between Mr Kerry, Iranian Foreign Minister Mohammad Javad Zarif and EU foreign policy chief Catherine Ashton came ahead of 20 July deadline for an agreement.
"We are working. We are working very hard. A lot of serious discussions. It was a good meeting," Mr Kerry told reporters after a two-hour meeting.
It was the second day of talks between Mr Kerry and Mr Zarif.
They are trying to narrow wide differences in negotiating positions over a deal intended to end a decade-long dispute over Iran's nuclear plans.
Iran says it is enriching uranium for peaceful energy purposes only and wants Western sanctions lifted.
However, a history of hiding sensitive nuclear work from UN inspectors has kept international suspicions high.
The White House has said Iran had engaged with Western powers in a serious way in the talks.
However, it said Iran had yet to make the decisions necessary to prove that its nuclear programme was ultimately peaceful.
White House spokesman Josh Earnest said Mr Kerry was assessing Iran's seriousness during the meetings in Vienna.
He said Mr Kerry would return to the US to make recommendations to US President Barack Obama on how to proceed.