Gholam Reza Aghazadeh had been due to travel to the International Atomic Energy Agency headquarters in Vienna on Monday for the talks, according to earlier state media reports.

"The trip has been postponed to an appropriate time that will be agreed on," IRNA quoted the public relations service of the Iranian Atomic Energy Organisation as saying.

The visit was to come after President Mahmoud Ahmadinejad sparked an angry international reaction on Tuesday with the announcement that Iran was working to install 6,000 more centrifuges at its Natanz uranium enrichment plant.

Western governments warned Tehran that it faces further sanctions if it continues to expand its nuclear programme, which they fear is cover for a drive to develop an atomic weapon.

But Iran insists that its nuclear programme is entirely peaceful and aimed solely at generating energy for a growing population whose supply of fossil fuels will eventually run out.

Iran says that it will discuss its nuclear programme only with the UN watchdog -- the International Atomic Energy Agency.

It insists there is no basis for involvement by the UN Security Council, which has already imposed three sets of sanctions over Iran's failure to heed repeated ultimatums to suspend uranium enrichment.

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