Iran's president hit back Saturday at President Obama's accusation that his country had sought to hide its construction of a new nuclear site, arguing that Tehran reported the facility to the U.N. even earlier than required.

The Iranian president defended his government's actions as the head of the U.N.'s nuclear monitoring agency, Mohamed ElBaradei, arrived Saturday to arrange an inspection of the uranium enrichment facility near the holy city of Qom.

The revelation that Iran has been building a new nuclear plant has heightened the concern of the U.S. and many of its allies, which suspect Tehran is using a civilian nuclear program as a cover for developing a weapons-making capability. Iran denies such a claim, saying it only wants to generate energy.

Obama and the leaders of France and Britain accused Iran of keeping the construction hidden from the world for years. President Obama said last month that Iran's actions "raised grave doubts" about its promise to use nuclear technology for peaceful purposes only.

ElBaradei, the head of the International Atomic Energy Agency, has also said Tehran was "on the wrong side of the law" over the new plant and should have revealed its plans as soon as it decided to build the facility.

President Mahmoud Ahmadinejad challenged that view in a speech Saturday, saying that Iran voluntarily revealed the facility to the IAEA in a letter on Sept. 21. He said that was one year earlier than necessary under the agency's rules.

"The U.S. president made a big and historic mistake," Iranian state TV quoted Ahmadinejad as saying. "Later it became clear that (his) information was wrong and that we had no secrecy."

Iran agreed to allow U.N. inspectors into the facility at a landmark meeting with six world powers near Geneva on Thursday that put nuclear talks back on track and included the highest-level bilateral contact with the U.S. in three decades.

Iranian officials argue that under IAEA safeguard rules, a member nation is required to inform the U.N. agency about the existence of a nuclear facility six months before introducing nuclear material into the machines. Iran says the new facility won't be operational for 18 months, and so it has not violated any IAEA requirements.

The IAEA has said that Iran is obliged under the Additional Protocol to the Nuclear Non-Proliferation Treaty to notify the organization when it begins to design a new nuclear facility.

Iran says it voluntarily implemented the Additional Protocol for 2 1/2 years as a confidence-building gesture, but its parliament passed legislation in 2007 forcing the government to end such cooperation after the country was referred to the U.N. Security Council for sanctions over its refusal to suspend uranium enrichment.

The IAEA has countered by saying that a government cannot unilaterally abandon such an agreement.

Suspicion that Iran's newly revealed nuclear site was meant for military purposes was heightened by its location, at least partly inside a mountain and next to a military base.

Iran has said it built the facility in such a way only to ensure continuity of its nuclear activities in case of an attack.

"Some are allowing themselves to threaten our legal facilities with military attack, and so we are going to come up with security measures for our nuclear facilities," Iran's senior nuclear negotiator, Saeed Jalili, said Friday after returning from the talks in Switzerland. "One of them is that we need to have a facility for uranium enrichment with a higher level of security and that's why we decided to establish the new facility that is under construction."

An IAEA spokesman said that in addition to the new nuclear facility, ElBaradei will also discuss a plan to allow Russia to take some of Iran's processed uranium and enrich it to higher levels to fuel a research reactor in Tehran.

Western officials said Iran agreed to the plan at Thursday's meeting, a potentially significant move that would show greater flexibility by both sides.

Obama noted the deal in comments on the meeting. But Mehdi Saffare, Iran's ambassador to Britain and a member of the Iranian delegation at the talks, said Iran had not yet agreed to such a plan.

The Obama administration, together with the U.S. Congress, is drawing up plans for tough new sanctions if the talks with Iran show signs of faltering. Obama said the new penalties could target Iran's energy, financial and telecommunications sectors.

A congressional committee will hold a hearing Tuesday on the possibility of expanding sanctions to cover a wider range of financial transactions, including a new ban on exporting refined petroleum to Iran.