"We have done nothing new and our activity is according to the regulations," said Iran's top nuclear official Mohammad Eslami, as quoted by the AFP news agency.
"We were producing the same 60 percent, we didn't change anything and we didn't create any new capacity."
On Tuesday, the IAEA released a report saying Iran "increased its production of highly enriched uranium, reversing a previous output reduction from mid-2023."
Iran had increased its output of 60 percent enriched uranium to a rate of about nine kilograms a month since the end of November, the UN watchdog said.
That is up from about three kilograms a month since June, and a return to the nine kilograms a month it was producing during the first half of 2023.
The United States said it is “greatly concerned” the IAEA report.
"Iran's nuclear escalation is all the more concerning at a time when Iran-backed proxies continue their dangerous and destabilizing activities in the region, including the recent deadly drone attack and other attempted attacks in Iraq and Syria and the Houthi attacks against commercial shipping vessels in the Red Sea," said a White House national security council spokesperson quoted by Reuters.
An IAEA report released in mid-November found that Iran has enough uranium enriched to up to 60% purity, close to weapons-grade, for three atom bombs.
A second report released at the same time found there has been no progress on the IAEA investigation into uranium traces found at several undeclared sites in Iran.
Iran a few months ago escalated the conflict with the IAEA by withdrawing accreditation from several top UN nuclear watchdog inspectors.
A standoff between Iran and the West, over the 2015 Iran nuclear deal, continues.
Iran has scaled back its compliance with the 2015 Iran nuclear deal in response to former President Donald Trump’s withdrawal from the agreement in 2018.
The Biden administration sought to return to the deal and held indirect talks with Iran on a return to compliance, but the negotiations reached a stalemate last September, after Iran submitted a response to a European Union proposal to revive the deal.
A US official later said that the efforts to revive the 2015 Iran nuclear deal have “hit a wall” because of Iran's insistence on the closure of the UN nuclear watchdog's investigations.