Some analysts who follow the Iranian sanctions say the timetable for achieving their desired result may not add up.
"What's clear is that Iran's nuclear red line will occur long before Iran's economic cripple date – when the regime faces imminent economic collapse as a result of sanctions," Mark Dubowitz, who is with the Foundation for Defense of Democracies, told CNN.
"That is the uncomfortable conclusion that the Obama administration must face: Iranian nuclear physics is beating western economic pressure," he said.
While the sanctions are designed to cripple the Iranian regime financially, the United States says the Iranian people must understand the sanctions are not designed to punish them.
"We want the Iranian people as well to understand that this is a direct response to the choices that their government has made in the context of the international community offering them a diplomatic way out," Nuland said, "which they should take."
The five members of the United Nations Security Council and Germany, the so-called P5+1 group that has been negotiating with Iran over its nuclear program, met last week on the sidelines of the General Assembly. The talks have been stalled for months.
EU Foreign Policy Chief Catherine Ashton will follow up by meeting with Saeed Jalili, Iran's senior nuclear negotiator, in the coming days, Nuland said, to decide whether another round of talks would be constructive.