Iran said on Monday it has formally told the UN nuclear watchdog of its plan to produce higher enriched uranium, sparking US and French calls for "strong" sanctions against the defiant Islamic republic.

"Iran's official letter about commencing the 20 percent enrichment activity in order to provide fuel for the Tehran reactor has been handed over to the IAEA," Ali Asghar Soltanieh, Tehran's envoy to the International Atomic Energy Agency, told state-owned television from its Vienna base.