Tehran is racing to keep its side of the deal reached with world powers in July, under which the sanctions that have battered its economy will be suspended in exchange for Iran severely limiting its nuclear program.
Iranian President Hassan Rouhani, who has overseen a thaw with the West, voiced hope on Wednesday that the sanctions would be removed in January, "delivering one of the electoral promises of the government" before elections on February 26.
International Atomic Energy Agency (IAEA) Director-General Yukiya Amano, whose agency must verify that Iran has put the required nuclear restrictions in place for sanctions to be lifted, told Reuters that deadline could be met.
"If everything goes well, it is not impossible," he said in an interview when asked if so-called Implementation Day, on which IAEA verification and the lifting of sanctions are both supposed to take place, could occur by the end of January.
Iran said after an IAEA board meeting on Tuesday that it hoped to have put the restrictions in place within two to three weeks. Amano has said his agency would then need a matter of weeks to verify the curbs.
On Wednesday, Amano confirmed that Iran was moving quickly to keep its side of the deal with the United States, Russia, France, Britain, Germany and China.
"Our inspectors are on the ground and they are observing their activities, and with their report I can tell that Iran is undertaking activities at a very high pace," Amano said, though he declined to provide details on those activities.
The restrictions Iran must put in place include drastically reducing the number of centrifuges installed at its underground enrichment sites, removing the core vessel of a reactor at Arak and shrinking its stockpile of enriched uranium.
"If your question is that Iran is planning to complete their preparatory activities in two, three weeks' time, I don't have a reason to doubt it," he said.
"If everything goes well it can go very smoothly, but if there's some mishandling it will take more time," he said. "It's difficult to say."
"WE ARE NOT INTERESTED"
Amano, who has headed the IAEA for six years, would also not be drawn on how long the agency would need for its verification, beyond that it would take weeks rather than days or months.
"If there are some small things, we need to do it again and it will take time," he said. "If everything goes well, it will be smooth. It's like any complicated endeavor."
Amano produced a report this month that strongly suggested Iran had a secret nuclear weapons program until 2003 and continued weapons-related work until 2009.
The report, which was drawn up under the July deal, received a muted response from major powers including the United States, which for years insisted Iran was lying when it said it had never sought the atom bomb.
Those powers had hoped the report would draw a line under whether Tehran's past activities had anything to do with nuclear weapons, clearing the way for the deal to be implemented, sanctions to be lifted and tougher checks put in place in Iran.
The IAEA's 35-nation Board of Governors decided on Tuesday to end its investigation of Iran's past, passing a resolution closing the matter by consensus, which means unopposed.
Beyond the board, Israel and some observers have said Iran's past activities should be investigated more thoroughly before sanctions against it are lifted, pointing to Iran's less than total cooperation with the IAEA.
The IAEA report said Iran had provided no new information on several outstanding questions since 2011, but Amano has said his agency had gained a better overall understanding of Iran's past activities since the deal with major powers.
"We don't assess attitude, we verify facts," he said. "Whether they have fully cooperated, 80 percent cooperated, that we don't say and we are not interested."