Three legal experts of the IAEA, the UN's nuclear watchdog, were holding talks with Iranian counterparts, said the spokesman of Iran's nuclear energy organisation, Saber Zaimian, quoted by IRNA.
Iran will decide in line with its "national interests" whether to accept snap inspections and submit its choice to supreme leader Ayatollah Ali Khamenei for final approval, a government spokesman said earlier in the day.
The Islamic republic is under strong international pressure to prove it is not secretly developing atomic weapons by signing an additional protocol to the nuclear Non-Proliferation Treaty (NPT).
The IAEA experts will explain the implications of Tehran signing the protocol, which would allow UN inspectors to descend without warning on suspect sites undeclared by Iran.
"After these people come to Iran and we listen to their reasons and justifications, then we will decide whether to sign the IAEA's additional protocol," Foreign Minister Kamal Kharazi said last week.
Iran insists that its nuclear programme is peaceful, and says that Western countries are bound by the NPT to assist it technically.
But Islamic conservatives warn that signing the additional protocol would sacrifice national independence to a Western "conspiracy".
Commentators have expressed anger that inspectors "acting on behalf of America, Israel and the EU" would go around "sticking their noses in all over the place" in Iran and helping "the conspiracy of America, its allies and the UN against the existence of the Islamic republic".
Opponents have gone as far as to call for Tehran to withdraw from the NPT altogether, with the conservative paper Entekhab (The Choice) splashing the headline "Growing Opposition to Signature of Additional Protocol" across five columns on Monday.
The newspaper said 500 students and lecturers from the influential Sharif technical university had written to President Mohammad Khatami calling on him "not to sign any agreement which would prevent Iran maintaining its absolute right" to use nuclear energy for peaceful purposes.
They received the support on Monday of Mahmud Hashemi Shahrudi, head of the judicial authority and seen as a key figure of conservative power.
"The Iranian leadership, with the support of the people, will not give in to pressure, and the representatives of the people and the students will resist America's aim to impose its will by force," he was quoted as saying by
A second IAEA team will carry out routine inspections before drawing up a report on Iran's nuclear facilities due to be released on September 8, the watchdog agency said last week.
Iran's representative at the Vienna-based IAEA has advised his government to agree to no-notice inspections and said he hoped the additional protocol will be signed by the agency's next board of governors meeting in September.
"We are currently in a situation in which the protocol can help us settle some problems and close the political file opened on our nuclear activities," Ali Akbar Saleh said in reference to the US-led criticism.
Last month, European Union foreign ministers expressed "increasing concern" over Iran's nuclear programme and demanded Iran's unconditional acceptance of the additional protocol.