A team of United Nations inspectors has begun a two-day visit to Iran for talks on its disputed nuclear programme.
The team said it was focused on "the possible military dimensions of Iran's nuclear programme”.
Several European countries have stopped buying Iranian oil, in a bid to add to the growing pressure on Tehran.
The Iranian government denies Western allegations that it is secretly trying to build nuclear weapons.
But today Iran deployed warplanes and missiles in an "exercise" to protect nuclear sites threatened by possible Israeli attacks and warned it could cut oil exports to more EU nations unless sanctions were lifted.
The European Union said it could cope with any halt in Iranian supplies.
The United States and Europe have ramped up economic sanctions against Iran's vital oil sector, while Israel has fuelled speculation it could be on the brink of carrying out air strikes on Iranian nuclear facilities.
Iran's military said today that it had launched four days of manoeuvres in the south aimed at boosting anti-air defences to protect nuclear sites.
Missiles, anti-aircraft artillery, radars and warplanes were deployed in the exercise dubbed "Sarollah”, a word borrowed from the Arabic meaning "God's vengeance”.
At the same time, the deputy oil minister, who also runs the National Iranian Oil Company, warned that a cut in Iranian oil exports announced yesterday against France and Britain could be expanded to other EU nations.
"Certainly if the hostile actions of some European countries continue, the export of oil to these countries will be cut," said Ahmad Qalebani, pointing the finger at Spain, Greece, Italy, Portugal, Germany and the Netherlands, Mehr news agency reported.
Iran exports about 20% of its crude - some 600,000 barrels per day - to the European Union, mostly to Italy, Spain and Greece.