Iran has agreed a timetable for nuclear inspections with the head of the UN's nuclear watchdog, Mohamed ElBaradei.
ElBaradei says he wants doubts over Iran dispelled once and for all
Mr ElBaradei said five hours of talks with Iranian officials had produced "welcome and positive steps" to end doubts about Iran's nuclear ambitions.
He said he had been assured he would receive the first batch of important information by the end of this month.
Iran suspended key inspections last month after the IAEA accused it of keeping nuclear activity secret.
Speaking after Tuesday's meeting with Mr ElBaradei, the head of Iran's Atomic Energy Association, Gholam Reza Aghazadeh, also pledged to speed up co-operation with the UN and satisfy all concerns about its programme by June.
Mr ElBaradei announced a new team of UN inspectors would arrive in Iran within days.
"We agreed that we need to accelerate the process of co-operation," Mr ElBaradei, head of the International Atomic Energy Agency (IAEA), said at a news conference after his talks with Mr Aghazadeh.
"Mr Aghazadeh committed that Iran will do everything possible to accelerate the
process of resolving the outstanding issues."
The Iranian nuclear chief told reporters that Tehran wanted "to bring this case to
a close" in June and announced it would "voluntarily" suspend centrifuge work from 9 April.
Mr Aghazadeh added that if ambiguities still existed, the agency should bring them up in the next few days so they could be resolved as quickly as possible.
June is when the IAEA's board of governors next meets to discuss Iran's progress regarding nuclear inspections.
The BBC's Miranda Eeles reports from Tehran that it is still unclear if the IAEA has enough time to compile a full report on Iran's nuclear activities ahead of its meeting.
Mr ElBaradei arrived in Tehran for a one-day visit on Tuesday with the task of pressurising Iran to be fully transparent in its dealings with IAEA.
Iran has been accused of keeping some of its nuclear activities secret (Image: DigitalGlobe)
It is his fourth visit to Iran in little over a year.
The US believes Iran is using its nuclear power programme to develop weapons while Iran insists it is just designed to meet its energy needs.
Before leaving for Iran, Mr ElBaradei said the authorities there had not been co-operating as openly and quickly as they should to dispel claims they wanted to build nuclear weapons.
He identified two key issues to be discussed: the origin of the highly enriched uranium found in the country and the purpose of nuclear centrifuges which could be used to produce weapons-grade material.
Last week Britain, France and Germany expressed concern over Iran's announcement that it was resuming uranium conversion - a crucial stage in the production of both nuclear weapons and nuclear fuel.
Iran hit back after the criticism, with UN ambassador Pirooz Hosseini telling Reuters that the plant near Isfahan was not in breach of Iran's commitment to suspend uranium enrichment.