"We have been able to have a much better understanding in a constructive atmosphere but there are differences on major issues," Deputy Iranian Foreign Minister Abbas Araqchi said in an interview with Kyodo News.
"Some of the ideas which (were) proposed in the New York meeting are still hopeful but none of them can provide us with a common understanding on key issues and we could not to make substantive progress in negotiations," he added.
"If it would be a deal, let's do it now, an extension would be useless and difficult," Araqchi said.
He indicated that the nuclear talks will resume in Vienna or Geneva in less than two weeks.
His comment came after Russian Foreign Minister Sergei Lavrov said in an interview with Bloomberg TV that the deal between the group 5+1 and Iran is 95 percent agreed.
"I think we are moving. We are moving in the right direction. Some 95 percent maybe of the deal, if you take the paper, which is being negotiated, is agreed. But the remaining 5 percent is where the devil is, two or three very difficult issues," Lavrov said.
"(The issues are) Difficult, I mean, they're resolvable, but difficult from the point of view of making a political decision to compromise on both sides," he added.
Nuclear negotiators representing Iran and the Group 5+1 (also known as the P5+1 or E3+3) held a new round of talks on Tehran’s nuclear program in New York this week. The negotiations were wrapped up on Friday night without making any tangible progress.
Iran and the six nations on November 24, 2013, signed an interim nuclear deal in the Swiss city of Geneva.
Based on the interim deal, the world powers agreed to suspend some non-essential sanctions and to impose no new nuclear-related bans in return for Tehran's decision to freeze parts of its nuclear activities.
In July, Tehran and the six countries agreed to extend negotiations until November 24 in the hope of clinching a final deal.