UN nuclear chief Yukio Amano said Monday that Iran is not cooperating with an investigation into suspected secret work on nuclear weapons.
Amano told the UN General Assembly on Monday that talks between the International Atomic Energy Agency and Iran have intensified this year.
"However, no concrete results have been achieved so far," he said.
In his annual report to the world body, Amano said he also remains "seriously concerned" about North Korea's nuclear program, calling its statements about uranium enrichment activities and the construction of a light water reactor "deeply troubling."
He also urged the Syrian government to respond to questions about a building destroyed by Israeli warplanes in the Syrian desert in 2007 which the IAEA says was "very likely" the covert site of a nuclear reactor.
Last week, Iran confirmed for the first time that it has finished installing centrifuges for enriching uranium at its underground nuclear facility in Fordo.
The head of Iran's Atomic Energy Organization, Fereydoun Abbasi, told Iran' Fars news agency on Thursday that "Iran is completing its nuclear activities regardless of the negative Western media speculations and reports." Abbasi spoke to reporters after a cabinet meeting in Tehran.
When asked about the recent media reports on Iran's new centrifuges in Fordo, located near the city of Qom, he said Iran is proceeding with its nuclear activities as scheduled.
"We are doing our job according to our specified timeline and we are accomplishing" our goals, Abbasi said. "Our response to such reports is working harder."
He was referring to a Reuters report a few days ago, which quoted Western diplomats as saying that Tehran would soon finish installing the last of the centrifuges planned for the Fordo facility. But the diplomats noted that for some unknown reason, the new centrifuges had not yet been activated.