The United States must lift the sanctions it has imposed on Iran in exchange for its return to the 2015 nuclear agreement, Iran's chief negotiator said on Sunday.

One of the main goals of the Vienna talks was "to establish the conditions that the Americans must meet," Ali Bagheri Kani, also Iranian deputy foreign minister, told official news agency IRNA in the Austrian capital.

Once those conditions are agreed upon, the Americans will have the duty to implement them, and the core requirement is the lifting of "the iniquitous and illegal sanctions," he added.

The positions of the parties in the talks are different on different issues, but during the last days the extension of the subjects open to the discussion has been reduced, Bagheri Kani noted. 

Speaking of the "non-constructive comments" from three European parties to the talks, the Iranian chief negotiator said he was optimistic about the future of the negotiations. 

However, the "hostile, illegal, destructive and even inhumane acts by some parties," as well as the existing mistrust, do not allow for any naivety concerning the process ahead, he added. 

Iran and other remaining parties to the 2015 nuclear deal, formally known as the Joint Comprehensive Plan of Action (JCPOA), started on November 29 the seventh round of talks in Vienna on the revival of the agreement, as the U.S. government under former President Donald Trump withdrew Washington from the accord in 2018.