The International Atomic Energy Agency (IAEA) head, Mohamed ElBaradei, on a flying visit to the Islamic republic to press for quick answers, said he received assurances of Iran's "readiness" to open up its suspect facilities.
"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 activities," ElBaradei told reporters after a meeting 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 however that Rowhani again reiterated "apprehensions" over allowing unhindered inspector access and its implications for Iranian sovereignty.
However ElBaradei added that Iran had still not agreed to stop enriching uranium.
The United States urged Iran to quickly sign a new non-proliferation protocol following ElBaradei's comments.
"From our point of view, we've made it clear that we expect Iran to sign the additional protocol without delay," State Department deputy spokesman Adam Ereli
EU leaders will tell Iran to agree rapidly to surprise UN inspections of its nuclear sites, the bloc's Italian presidency said Thursday.
In draft conclusions to a two-day EU summit in Brussels unveiled to journalists by Italian Foreign Minister Franco Frattini, the leaders "reiterated the need for the rapid ratification" by Iran of an additional protocol to the nuclear Non-Proliferation Treaty allowing unscheduled checks of suspect facilities.
Germany, France and Britain could cooperate with Iran's nuclear energy programme if Tehran shows the international community it is not hiding a covert weapons scheme, a Western diplomatic source told AFP Thursday.
The countries would also insist Iran accept strict controls on its nuclear activities, said the diplomatic source, who added that senior representatives of the countries had arrived here in recent days to "resolve this crisis peacefully."
The IAEA has been pressing Iran to sign the additional protocol to the nuclear Non-Proliferation Treaty (NPT), which would give the watchdog the right to carry out unannounced inspections of suspect facilities.
The agency has also given Iran until October 31 to answer questions on its nuclear programme.
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.
Non-compliance by Iran could lead the IAEA to take the issue to the UN Security Council, which could then impose punishing sanctions on Tehran.
Hoping to avoid that, Iran's representative to the IAEA said cooperation would be stepped up -- a departure from the angry rhetoric heard in Tehran after the resolution was passed on September 12 after heavy US lobbying.
"In the coming days, the rhythm of our cooperation will accelerate considerably," Ali Akbar Salehi told AFP. "I hope that we can move past this political and artificial crisis."
Despite the Iranian assurances, ElBaradei spoke of "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".
Talks on the protocol with IAEA experts will begin Saturday, he said.
Prior to his arrival Wednesday night in Tehran, ElBaradei accused Iran of dragging its feet ahead of the deadline, saying it had yet to give IAEA inspectors all the information they need.
"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.
Washington accuses Iran of trying to develop nuclear arms and has branded it part of an "axis of evil", along with Saddam Hussein's Iraq which it said held weapons of mass destruction, and North Korea, which has said it is making atomic bombs.
ElBaradei said it was crucial that Iran answer questions about enriching uranium which could be used to make atomic weapons.
ElBaradei is due to report back on November 20 to his council of governors, the IAEA's executive organ.