He told reporters he would tell the International Atomic Energy Agency's (IAEA) 35-nation board that began meeting in Vienna Monday that Iran's cooperation has "been less than satisfactory and I'm calling on them obviously and expect the board also to call on them to become more transparent and more pro-active."
"It is essential for the integrity of the (international nuclear) safeguards operations that we should bring this issue to a close in the next few months," ElBaradei said.
"I think everybody would like to see this issue brought to a close... because we can not go on forever," he added.
However the UN official seemed to reject the idea of imposing a deadline on Iran when he said that finishing the investigation involved "technical issues. It is not a political issue by which you can set a particular date or month."
ElBaradei said the extent of Iran's uranium enrichment activities was the central issue to be resolved.
"We still have a central issue and that is whether Iran has declared all its enrichment activities," he said.
ElBaradei said two main questions to be resolved regarding enrichment were HEU "contamination we found in some equipment and the question of advanced P-2 centrifuges" which can be used to make bomb-grade uranium.
Highly enriched uranium can be used as fuel for a civilian nuclear reactor, but also in building an atomic bomb.
The United States charges that Iran is secretly trying to develop nuclear weapons and should be taken to the UN Security Council for possible sanctions.
But Washington does not have support at the IAEA for its hardline stance and the board was set to consider a British-French-German draft resolution to rap Iran for failing to fully disclose its nuclear activities but to call for further cooperation in the investigation.
The IAEA has been investigating the Iranian program since February 2003 and reporting to the board on it for the past year. Iran claims its program is strictly peaceful and had wanted the investigation to be brought to a close this June.
Iran was defiant as the IAEA meeting began. The country is preparing itself for a souring in ties with the IAEA as Tehran refuses to renounce its right to enrich uranium for nuclear fuel, Seyed Hossein Mussavian, a member of Iran's Supreme National Security Council, told the Iranian student news agency ISNA Sunday.
"We are entering into a second phase which is the challenge posed by enrichment," Mussavian said, adding that this was difficult since "the Americans and the Europeans are on the same side".
"The Europeans are saying that in order to be sure that nuclear fuel is not used to produce nuclear weapons, Iran must renounce enrichment.
"But Iran considers enrichment to be an absolute right in the Non-Proliferation Treaty (NPT) and Iran is not ready to renounce this," Mussavian said.
Tehran has agreed to suspend enrichment as a confidence-building measure but has insisted the suspension is only temporary and continued to work on other key parts of the sensitive nuclear fuel cycle.
Mussavian said the British-French-German draft resolution signifies "that the Europeans, the IAEA and the Americans have a tacit agreement to keep the dossier at the top of the agenda so that the suspension of enrichment is longer."
He demanded it be amended, and Iranian diplomats were lobbying for this in Vienna.
"Everyone realizes what's at stake," a diplomat close to talks on the resolution told AFP about the need to determine whether Iran is hiding a nuclear weapons program, as the United States claims, or developing nuclear power for peaceful purposes, as Tehran says.