At an international nongovernmental conference here marking the 60th anniversary of the first official nonproliferation proposal, ElBaradei said Tehran must come clean on its nuclear intentions.

"Over the past two and half years, we have compiled a detailed picture of most aspects of Iran's past and current nuclear program," ElBaradei said, according to an advance transcript of his remarks.

"But given that the program was concealed for nearly 20 years, and that a number of open questions remain, the responsibility rests with Iran to provide, if needed, additional transparency measures," ElBaradei said.

The UN's nuclear watchdog chief is due to meet US Secretary of State Condoleezza Rice Tuesday. Rice has said Washington -- which views Iran as a state sponsor of terrorism -- is opposed to Iran obtaining nuclear weapons.

ElBaradei said that improved transparency from Tehran would "enable the (UN) agency to resolve these questions, and to provide the required assurance about the peaceful nature of Iran's nuclear program."

ElBaradei's remarks come one day after Iran formally asked Britain, France and Germany to reopen the stalled nuclear talks with the 25-member European Union, which broke off in August when Tehran, under new hardline president Mahmoud Ahmadinejad, resumed uranium conversion in defiance of international calls to maintain a suspension.

Iranian officials have said the Islamic Republic would convert a fresh batch of uranium ore in a rejection of EU calls for a renewed freeze on such activities.

The European Union said Monday it was studying Iran's new offer to resume talks on Tehran's disputed nuclear programme.

British Foreign Secretary Jack Straw, one of three EU ministers who have led efforts to engage Iran by offering benefits in return for pledges on its nuclear plans, said the bloc will reply shortly to Tehran's offer.

ElBaradei's keynote speech opened the Carnegie International Non-Proliferation Conference Monday.

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