"I hope that Iran will go back to a comprehensive suspension as they have committed to us before. I would hope that this is not a major reversal," he told reporters after meeting Russian atomic energy agency chief Alexander Rumyantsev.
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.
The IAEA is investigating US charges that Iran is secretly developing nuclear weapons.
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 International Atomic Energy Agency (IAEA) close in June its investigation of Iran's nuclear program, in return for the suspension of all enrichment-related activities.
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.
ElBaradei told Iran on Sunday to stop complaining about Europe and focus on cooperation with the IAEA.
ElBaradei told journalists his message to Iran was: "Stop looking anywhere else. You need to look at the agency. You need to cooperate with us."
"I don't think these issues are going to be resolved through confrontation. I think these issues are going to be resolved by steady engagement and robust verification," ElBaradei said.
ElBaradei opened an IAEA nuclear power conference 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.
It also marks the 50th anniversary of the UN General Assembly resolution calling for international cooperation in developing the peaceful uses for nuclear energy.
"The factors that will shape the future of nuclear power are relatively evident and we should take action ... to enhance the prospects that nuclear energy remains a viable source of safe, secure and environmentally benign energy," ElBaradei said.
In particular, he mentioned the need to improve technology to keep reactors safe.
ElBaradei said 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.
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.
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.
But atomic energy agency chief Alexander Rumyantsev told reporters that Iran was cooperating with the IAEA and so "Russia cooperates with Iran in the construction of the first nuclear power plant unit in Bushehr."
He said Russia will "speed up negotiating" over supplying nuclear fuel to Iran for Bushehr in order to meet contractual deadlines.