Nuclear talks between Iran and world powers continue on July 16 in Vienna amid suggestions about a possible extension of negotations beyond a July 20 deadline.
Iranian Foreign Minister Mohammad Javad Zarif said on July 15 that after two days of talks progress had been made, but added that "more time may help."
U.S. Secretary of State John Kerry said separately that "tangible progress" had been achieved after "tough negotiations," but stressed that "very real gaps" remain in the positions of the two sides.
However, both Zarif and Kerry said that they still hoped to secure a deal by the July 20 deadline.
U.S. President Barack Obama and German Chancellor Angela Merkel in a phone call on July 15 agreed it was "imperative" for Tehran to prove that its nuclear program will be "exclusively peaceful."
The P5+1 group of world powers want Iran to reduce the scope of its enrichment program in exchange for the lifting of sanctions, while Tehran wants to expand it.