Talks between the U.S. and Iranian teams reached the 15-hour mark on Saturday and were likely to continue on Sunday, according to The New York Times.
IRNA, Iran's state news agency, and two senior Iranian officials apparently confirmed the negotiations had hit a deadlock.
"The Strait of Hormuz remains a sticking point in the talks, with the U.S. demanding an immediate opening of the chokepoint and Iran doubling down on its stance that the economically vital passageway will re-open only after a final peace deal is reached, according to the two officials, who spoke on the condition of anonymity," The Times reported.
The American delegation has not yet commented on the status of the ongoing negotiations.
More than a month since the war started, the historic high-level talks were the first between the two countries since the 1979 Islamic Revolution.