"Review of annexes and documents is almost done. There are some key remaining issues — if we can overcome them, we can have a final agreement. We don't accept any deadline in the talks. Americans had their own deadline," the source said.
"There are times that you see an understanding is reached but then they [the United States] change their position and they have excessive demands, which we resist…We will continue negotiations until we come to a conclusion," the source said.
In April 2015, the sides reached a breakthrough framework agreement, stipulating that Iran should decrease its uranium enrichment and the number of centrifuges in exchange for gradual easing of economic sanctions imposed on the country.
The deadline for striking a final deal has been repeatedly postponed.