The move would help the UN to adopt harsher sanctions on Iran, which had refused to stop its uranium enrichment last month before the IAEA report was released, the report said.

Many Russian experts had reportedly left to Moscow as recently as last week, and this move was believed to be associated with the final disagreement between Russia and Iran on financial issues.

Sergei Novikov, a spokesman for the Russia's Federal Nuclear Power Agency Rosatom, confirmed the issue, saying the reason was Iranian payment delays.

Russia yesterday denied US press reports that it had threatened to withhold nuclear fuel for Iran's Bushehr nuclear plant if Tehran fails to meet UN demands to suspend uranium enrichment.

"I can tell you that the report is not accurate, that there has been no Russian ultimatum to Iran of any kind," Russian Ambassador to the UN, Vitaly Churkin, told reporters.

"We continue to regard the Bushehr project as something that is outside the scope" of the UN sanctions resolutions