The meetings in New York were confirmed by Iranian state media:
"The foreign minister of our country will meet with Qatar's (representatives), who are mediators between the US and Iran."
Iran's delegation is expected to return to Tehran on Tuesday.
The United States has also held talks with the Qatari mediators outside the official schedule during the UN General Assembly.
The American media company Axios says that Donald Trump is prepared to release frozen assets and ease sanctions against Iran in return for promises regarding Iran's nuclear energy programme.
Trump responded late on Monday that he had not promised Iran anything, and that the information was a "hoax."
