It will be the third visit to Iran by ElBaradei, the director general of the International Atomic Energy Agency, since the IAEA began in February 2003 investigating whether the Islamic Republic was secretly developing atomic weapons, as the United States alleges.
The purpose of the visit is "to consult on outstanding issues relevant to the IAEA's verification of Iran's safeguards agreement" under the nuclear Non-Proliferation Treaty (NPT), Fleming said in a statement.
She had told AFP last week: "With the IAEA board of governors members calling for a comprehensive report for the next board meeting in June, Dr ElBaradei wants to personally emphasize to the Iranians how crucial it is they act in a fully transparent and cooperative manner so that the open questions about Iran's nuclear activities can be answered."
Two IAEA inspectors arrived in Iran last Saturday to carry out more checks on the country's nuclear program.
Iran had tried to put off the mission earlier this month after the IAEA condemned it for continuing to hide sensitive nuclear activities including designs for sophisticated P2 centrifuges for making enriched uranium which could be weapon-grade.
But Tehran yielded and allowed the visit after a delay of two weeks, following an international outcry against Iran for failing to cooperate with the atomic agency.
The UN team will focus its inspections on the Natanz uranium enrichment plant and the Isfahan nuclear technology centre.
The Natanz plant is one of two sites where IAEA inspectors have discovered traces of highly enriched uranium. This substance can be used in civilian nuclear reactors to generate electricity but it can also be used as raw material for a nuclear bomb.
Isfahan is a nuclear technology centre with a uranium conversion facility.
Inspection missions later in April are to verify Iran's pledge to suspend uranium enrichment and to try to answer questions about whether Iran has tried to make P2 centrifuges or has designs for nuclear weapons, diplomats said.