Barack Obama, the new US president, has signalled that Washington may be willing to talk to Tehran over the two countries' relations.
The United Nations has demanded Iran suspend its enrichment programme over fears it could be used to produce nuclear weapons.
Iran denies the charge, saying its programme is only for generating electricity.
Despite a six-year investigation, the IAEA has been unable to determine whether or not Iran's uranium enrichment programme is intended for peaceful purposes.
ElBaradei said that Iran was stonewalling on key questions that could give insight into its intentions.
"The agency regrettably was unable to make any progress on the remaining issues which give rise to concerns about possible military dimensions of Iran's nuclear programme because of lack of co-operation by Iran," he said.
"For the agency to be able to make progress, Iran needs to provide substantive information and access to relevant documentation, locations and individuals in connection with all of the outstanding issues."
On Monday, Tehran again denied that it harbours nuclear ambitions, after Admiral Mike Mullen, a top US military commander, claimed Iran has enough fissile material to build an atomic bomb.
"All this talk is baseless," Hassan Ghashghavi, a foreign ministry spokesman, said.
"For that to be true, two things would have to happen... first, Iran has to exit the [nuclear] NPT [non-proliferation treaty] and second, it should be proved that Iran is seeking high-enriched uranium," he said.
Last week, Iran said it ran a successful test run of its Russian-built nuclear power plant, in the southern port city of Bushehr.
Moscow, which is supplying fule for the reactor, has said the it would not be used for military goals.
Ghashghavi said on Monday that Sergei Shmatko, the Russian energy minister, will visit Tehran in the next few days.
His trip is expected to focus on nuclear energy co-operation between the two countries.