US Secretary of State John Kerry has said that America and other major powers are not in a rush to reach a nuclear agreement with Iran.
But he warned that the so-called P5+1 (US, UN, Russia, UK, France and Germany) would not wait indefinitely.
Meanwhile, Iranian Foreign Minister Mohammad Javad Zarif tweeted: “We’re working hard, but not rushed, to get the job done.”
The pace at which sanctions are lifted is a major issue at talks in Vienna.
Pressure is mounting on world powers and Iran to reach a deal on its nuclear programme and avoid the issue becoming bogged down in the US Congress.
Congress has 30 days to review any agreement as long as it receives the text by midnight Washington time (04:00 GMT on Friday). Failing that the review period will be 60 days, which will delay the lifting of US sanctions.
