Iran's nuclear chief, Gholamreza Aghazadeh, has begun talks in Vienna with the International Atomic Energy Agency.
The meeting between Aghazadeh and a top IAEA deputy comes two days before the agency is to file a report on Iran's nuclear activities with the U.N. Security Council.
The Security Council has demanded that Iran stop enriching uranium, which can be used to power nuclear reactors or atomic bombs.
Both the United States and the European Union have accused Tehran of seeking to develop a nuclear arsenal. Iran denies the charges.
Earlier Wednesday, Iranian Supreme Leader Ayatollah Ali Khamenei warned that U.S. interests around the world will be harmed if the United States launches an attack on the Islamic Republic. The Iranian news agency quotes the ayatollah as saying U.S. interests in every possible corner of the globe will be targeted.
On Tuesday, the ayatollah said Iran is prepared to share nuclear technology with other countries.
Separately, Iran's top nuclear negotiator, Ali Larijani, warned that Tehran would stop cooperating with the U.N. nuclear agency if the Security Council imposes sanctions against Iran.
Some information for this report was provided by AFP, AP and Reuters.
