On arriving here Saturday ElBaradei called on Iran to reconsider its decision to abandon a pledge made in February not to build, assemble and test centrifuges.
Tehran said Sunday it would resume construction of centrifuges for uranium enrichment but continue to suspend enrichment itself, a key step in making what can be bomb-grade uranium.
Iran had said in a letter to ElBaradei, as well as Britain, France and Germany, last week that it would resume the "manufacturing of centrifuge components and assembly and testing of centrifuges as of June 29," next Tuesday, according to a copy of the letter obtained by AFP.
Iran claims the so-called Euro-3 broke an agreement made in February to have the IAEA close in June its investigation of Iran's nuclear program, in return for the suspension of all enrichment-related activities.
"I hope Iran will go back to full suspension" of uranium enrichment activities, ElBaradei said Saturday.
This suspension was part of confidence-building measures which Iran has been urged to take while the IAEA investigates US charges that the Islamic Republic is secretly developing nuclear weapons.
The 35-nation board of the IAEA passed a resolution on June 18 rebuking Tehran for failing to come clean about its nuclear program, deploring the level of Iranian cooperation and calling for the 15-month-old investigation into Iran's nuclear activities to be wrapped up within a few months.
The IAEA nuclear power conference here will be commemorating "a half-century since the Obninsk power reactor (120 kilometres/70 miles south of Moscow) became the world's first to produce electricity for a national grid and the 50th anniversary of the UN General Assembly resolution calling for international cooperation in developing the peaceful uses for nuclear energy," an IAEA spokesman said.
Nuclear expert Alan McDonald told reporters at IAEA headquarters in Vienna last week that atomic energy definitely had a future, despite concerns brought on by the Three Mile Island and Chernobyl nuclear accidents in the United States in 1979 and and in Ukraine in 1986.
Environmentalists condemn the use of nuclear energy for power, citing the danger of radiation from accidents and the problems of disposing of highly radioactive spent fuel.
But nuclear power use is growing in Asia while it continues to play a role in Western power supplies.
Besides the economics of years of cheap energy once a plant has been built, the environmental advantage of nuclear energy, provided reactors don't explode and waste doesn't seep into water supplies, is that "nuclear power emits virtually no greenhouse gases," the IAEA said in a report on "Nuclear Power's Changing Future."
Another theme at the conference will be nuclear terrorism.
The United States had at IAEA headquarters in Vienna in May unveiled a 450-million-dollar plan to try to prevent nuclear materials stored around the world from falling into the hands of terrorists who could use them to make a "dirty" bomb or even a full-fledged atomic device.
The US plan includes working with Russia "to repatriate all Russian-origin fresh HEU (highly enriched uranium) (nuclear) fuel by the end" of 2005, Energy Secretary Spencer Abraham had told the IAEA in May.
Daniil Kobyakov, from the PIR think tank in Moscow, told AFP: "Nuclear terrorism is a great concern here, and there is also concern about nuclear materials in Russia itself."
ElBaradei will be meeting in Moscow with Russian President Vladimir Putin as well as Foreign Minister Sergei Lavrov, atomic energy agency chief Alexander Rumyantsev and Security Council chairman Igor Ivanov.
Russia has been under US pressure to halt construction of Iran's Bushehr nuclear reactor until the IAEA is fully satisfied that Tehran is not hiding its potential nuclear weapons ambition, or using the project to develop an atomic bomb.
Russia has vowed however to maintain the Bushehr project.