Iran has told the International Atomic Energy Agency (IAEA) it will not allow two of its inspectors to enter the country, state media report.
The head of Iran’s Atomic Energy Organisation, Ali Akbar Salehi, said they had prematurely published a report he described as “untruthful”.
Mr Salehi did not say which parts of the report he considered inaccurate.
The decision comes two weeks after the UN Security Council voted to impose a fourth round of sanctions on Iran.
US President Barack Obama said the punishment, for continuing to defy resolutions ordering it to suspend all enrichment of uranium, was an unmistakable message on stopping the spread of nuclear arms.
Iran’s President Mahmoud Ahmadinejad said the sanctions should be thrown in the dustbin like a “used handkerchief”.
The US and its allies fear Iran is trying to build a nuclear bomb, but Tehran insists its nuclear programme is solely for peaceful purposes.