Multiple rounds of international sanctions are failing to have any effect on Iran's controversial nuclear programme, the head of the UN atomic agency said on Tuesday.
"We are verifying the activities at the nuclear sites in Iran and we do not see any effect," International Atomic Energy Agency (IAEA) head Yukiya Amano said in Paris.
"They are for example producing enriched uranium up to five percent and 20 percent with a quite constant pace."
Uranium enrichment lies at the heart of the international community's concerns about Iran's nuclear programme, since the material produced can be used not only for peaceful purposes -- Iran's stated intention -- but also, when further treated, for a nuclear bomb.
Enriched to five-percent purities, uranium can be used for power generation, and to 20 percent for medical purposes. But when further enriched, a relatively easy process, it can go in a weapon.
The UN Security Council has passed six resolutions calling on Iran to suspend all enrichment, passing four rounds of sanctions.
Amano's comments follow the release of the IAEA's latest report on Iran on Friday.
It said Tehran was on the threshold of being able to triple its monthly production of 20-percent-enriched uranium after completing the installation of machinery at its Fordo site, dug into a mountain near the holy city of Qom.
Amano also said that it was "difficult to predict" whether Iran and the IAEA will make progress in their next round of talks in Tehran on December 13 following a string of fruitless earlier meetings.
The talks are aimed at persuading Iran to respond to "overall, credible" claims set out in a major IAEA report a year ago that until 2003 and possibly since, Tehran conducted nuclear weapons research work.
On Wednesday in Brussels meanwhile, six world powers -- Britain, China, France, Russia, the United States, and Germany -- are due to hold their first talks since the US presidential election on November 6 ahead of a possible new round of talks with Iran, possibly before the end of the year.