By Mick Krever, CNN
(CNN) - An "understanding or agreement" on Iran's nuclear program may be possible as soon as Friday, Foreign Minister Javad Zarif told CNN's Christiane Amanpour on Thursday.
"We know what the ingredients should be. We have discussed them in the last three, four weeks. And I think our colleagues are ready to start drafting," Zarif, Iran's chief nuclear negotiator, said. "I believe it is possible to reach an understanding or an agreement before we close these negotiations tomorrow evening."
Direct negotiations resumed on Thursday between Iran and the so-called P5+1 - Germany plus the permanent five members of the U.N. Security Council: The United States, the United Kingdom, France, Russia and China.
Iran is seeking relief from the Western sanctions that have inflicted serious damage on its economy; the West wants to prevent Iran from acquiring a nuclear weapon.
"There won't be a suspension of our enrichment program in its entirety," Zarif said. "But we can deal with various issues - various issues are on the table."
At issue is whether Iran will stop enriching uranium entirely or continue to produce nuclear fuel for civilian and research use, as allowed under the Nuclear Non-proliferation Treaty.
In an interview with Amanpour on Wednesday, U.S. Senate Democrat Bob Menendez called on Iran to suspend its uranium enrichment.
"It's not rolling back its 20% or 3.5% enrichment," Menendez said. "It's not reducing its centrifuges. Why can you not simply suspend in order to have the negotiation that you want? That would be a good-faith effort."
Zarif rejected that idea.
"Iran suspended its entire enrichment program from 2003 to 2005," he said. "So we've tested that. And it didn't produce positive results. We're not going to test that again."
"We've got to be creative, we've got to be innovative and deal with situations as - on the basis of realities, not on the basis of illusions," he told Amanpour. "I believe, at the end of the day, everybody will be happy with a deal that can be achieved today."
The foreign minister would not go into further detail about what elements were being discussed, saying that the negotiations were at a "very sensitive stage" and were best held behind closed doors."
"We are prepared to address some of the most immediate concerns that have been raised," Zarif said. "And then we expect reciprocally for our concerns to be met by the P5+1, particularly the United States and the European Union."
Nothing is yet on the table, he told Amanpour, but "everybody knows where the concerns are."
It is now a matter of starting to draft the actual text of an agreement.
"I believe the ingredients are there," he said. "It takes quite a bit of effort, and quite a bit off good faith and political will. I know that we have it on our side, and I hope that we can expect the same from the other side."
He said that policy of imposing pressure, which included sanctions, had "produced no results" - adding that in about 10 years, Iran had increased its number of centrifuges from "160" to "19,000."
"There is a window of opportunity now that has been created by the Iranian people through their election of President [Hassan] Rouhani," Zarif said. "And that opportunity needs to be seized."
UPDATE: This article was updated with stylistic changes throughout.