"I was assured... that the Islamic Republic of Iran will clarify all the outstanding issues for us to be able to verify all aspects of its nuclear activites," Mohamed ElBaradei told reporters after talks with Hassan Rowhani, the secretary of Iran's Supreme Council on National Security.
"He expressed the readiness of Iran to sign the additional protocol," ElBaradei said, adding that Rowhani again reiterated "apprehensions" over allowing unhindered inspector access and its implications for Iranian sovereignty.
The IAEA has been pressing Iran to sign the additional protocol to the nuclear Non-Proliferation Treaty (NPT), which would give the IAEA the right to carry out unannounced inspections of suspect facilities.
Despite the Iranian assurances, ElBaradei said there were still "a number of outstanding issues and technical issues that we need clarification on."
He added: "I hope we will be able to clarify these issues and get a satisfactory answer."
In his own brief comments, Rowhani said Iran did have "a certain number of apprehensions" over the additional protocol, but he added: "I am not pessimistic".
He said that talks on the protocol with IAEA experts would begin Saturday.
ElBaradei said he had also sought to assure Rowhani that "these apprehensions are unfounded."
"The protocol is never meant in anyway to compromise state sovereignty, dignity, security or technical development. That is not the purpose of the protocol," the IAEA chief, who is in Tehran for a day of talks, told reporters.
The IAEA has given Iran until October 31 to answer questions on its nuclear program. It began an intensive round of inspections on October 1, and ElBaradei has revealed that military as well as civilian sites have been visited. He has also said the deadline will not be extended.
Prior to his arrival Wednesday night in Tehran, ElBaradei accused Iran of dragging its feet ahead of the deadline, which is less than two weeks away, saying it had yet to give IAEA inspectors all the information they need.
"We have been making progress but not with the speed we would like to see," ElBaradei told reporters late Wednesday while travelling to Iran.
"Iran has been offering us additional information, additional access but not the 100 percent transparency and not the pro-active cooperation I would like to see if we were to be able to get full information we need by the end of the month," ElBaradei said.
Non-compliance by Iran could lead the UN's nuclear watchdog to take the issue to the UN Security Council, which could then impose punishing sanctions on Tehran.
Washington accuses Iran of trying to develop nuclear arms and has branded it part of an "axis of evil", along with the Iraq of Saddam Hussein that it said held weapons of mass destruction, and North Korea, which has claimed it is making atomic bombs.
ElBaradei said it was crucial that Iran provide full disclosure on its nuclear program, particularly answering questions about enriching uranium which could be used to make atomic weapons.
"I got an invitation from the Iranian authorities telling me that it would be very important for me to visit at this stage," ElBaradei said late Wednesday. "I am ready obviously to walk the extra mile if we can bring the issue to closure as soon as possible."
ElBaradei said Iran had not yet indicated from which countries it had imported the equipment Tehran claims is the source of highly enriched uranium particles found by IAEA inspectors.
The United States claims that these particles do not come from contaminated equipment from abroad but are in fact proof that Iran is making highly-enriched uranium.
ElBaradei is due to report back on November 20 to his council of governors, the IAEA's executive organ.