Iran has demanded the removal of the UN official in charge of inspecting the country's nuclear programme, diplomats have said.
Iran has already banned 38 nuclear inspectors
The official, Chris Charlier, has already been banned from entering Iran.
Iran has the right to reject inspectors from the UN's nuclear agency, the IAEA, that it does not want.
There are growing international fears Iran is trying to build nuclear weapons. Iran says its nuclear programme is for peaceful uses only.
In a letter to the International Atomic Energy Agency (IAEA) headquarters in Vienna, Iran's government is reported to have also demanded that Mr Charlier not be allowed to see any reports on Iran.
The move follows a ban on 38 inspectors from four countries that Tehran imposed on Monday.
The inspectors are from key Western nations that had pushed for UN sanctions against Iran for refusing to stop enriching uranium.
The head of the IAEA, Mohamed ElBaradei, said there will still enough inspectors left in Iran to do the job.
He called for a "timeout" in the standoff over Iran's nuclear programme, saying "Iran should stop enriching uranium and the international community should take a timeout from implementing sanctions".
Iran has announced plans to install 3,000 centrifuges at its Natanz nuclear facility. This would be a massive increase in its potential to produce enriched uranium.
Centrifuges are the machines that spin uranium gas to enrich it to low levels for fuel and much higher levels for nuclear weapons.