Iran's proposal for a tour of its nuclear sites floundered on Thursday after China effectively rejected the invite and Russia cautioned such a trip could never replace UN inspections or talks between Tehran and world powers.

The European Union has turned down Iran's offer to allow selected ambassadors accredited to the UN nuclear watchdog to visit two nuclear installations while the United States, Britain, France and Germany were not even invited on the trip.

China, ahead of President Hu Jintao's state visit to the United States next week, said that it would be 'difficult' for its ambassador to the International Atomic Energy Agency (IAEA) in Vienna to go on the proposed tour.

'The Vienna representative is still in China right now, so it will be difficult for him to go to Iran,' Foreign Ministry spokesman Hong Lei told a news briefing, without elaborating.  

Just hours later, Russian Foreign Minister Sergei Lavrov told reporters in Moscow that such a visit could never replace regular inspections from the IAEA or talks with major powers on Iran's disputed nuclear programme, echoing the EU position.   

'Such a visit should in no way at all be seen as a substitution for IAEA inspections,' Lavrov said, though he said the invitation deserved attention. He did not give a clear indication of whether Russia would agree to the tour.

Several UN Security Council resolutions have urged Iran to allow unrestricted inspections to defuse mistrust in Tehran's stance that it is enriching uranium only for electricity and other peaceful purposes, not for nuclear weapons.

Without the European Union, China and possibly even Russia, Tehran's trip proposal could collapse before Istanbul talks next week between Iran and the so called P5+1 group -- the five permanent members of the Security Council along with Germany. - Reuters