The official said that gaps remain between the United States and Iran and that "it could take a little longer" to come to a final agreement, if one is possible.
"We’re studying Iran’s response now and we'll get back to them soon," the official said.
Earlier, State Department spokesman Ned Price said there was no guarantee a deal can be struck, saying "the outcome of these ongoing discussions still remains uncertain as gaps do remain." Washington would have to lift some sanctions under the terms of the agreement, but U.S. officials say returning to the deal is crucial to preventing a nuclear crisis in the Middle East.