Senior US officials say progress has been made in talks between Iran and the six major powers over Tehran\'s nuclear program, but stressed Iran needs to follow talks with positive actions. \"How far we get ... depends on what the Iranians come back with in terms of a response on the substance to our proposal,\" said a senior US official, who spoke on condition of anonymity, ahead of the \"Almaty 2\" talks in Kazakhstan, between Iran and the P5+1, which include the United Kingdom, China, France, Germany, Russia and the United States. \"There has been a very positive line out of Tehran on the talks so far. We hope that that positive talk will now be matched with some concrete responses and actions on the Iranian side,\" the official added. The United States and its allies suspect Iran of using its civilian nuclear program as a cover to develop atomic weapons. Iran denies this, saying its program is entirely peaceful. At February 26-27 talks with Iran in Almaty, Kazakhstan, the six major powers offered modest sanctions relief in return for Iran curbing its most sensitive nuclear development. \"I would hope that we\'re not at any last chance,\" said the official. \"If we are not sure about how much we\'ve gotten and whether we have gotten enough, we\'ll go back and consult with capitals before we reach any ultimate conclusion here. \"So I think we have time and space to consider what we hear,\" the official added. \"We hope that they make concrete, substantive and specific responses so that we can go to work.\" In February, western officials said the offer presented then by the six powers included an easing of a ban on trade in gold and other precious metals, and a relaxation of an import embargo on Iranian petrochemical products. In exchange, a senior US official said, Iran would, among other things, have to suspend uranium enrichment to a fissile concentration of 20 percent at its Fordow underground facility and \"constrain the ability to quickly resume operations there.\" This appeared to be a softening of a previous demand that Iran ship out its entire stockpile of higher-grade enriched uranium, which it says it needs to produce medical isotopes. Iran says it has a sovereign right to enrich uranium for peaceful purposes, and wants to fuel nuclear power plants so it can export more oil.