Russia is one of six world powers considering Iran's offer of “serious negotiations” over its controversial nuclear programme. Iran says it is ready to begin talks as early as Wednesday.

The offer is part of Tehran's response to incentives aimed at persuading it to scale back its nuclear ambitions. The United Nations has given Iran until the end of August to freeze its uranium enrichment programme, or face possible sanctions.

Washington has accused Iran of secretly trying to develop nuclear weapons – a charge Tehran has always denied.  Meanwhile, nuclear industry officials from Iran travelled to Moscow for training, heading for the Kalinin nuclear power plant in central Russia.