Iran has doubled capacity at its Fordo nuclear site, according to the latest quarterly report from the International Atomic Energy Agency (IAEA), the United Nation's nuclear watchdog.

The IAEA also noted that Iran had "significantly hampered" the ability of monitors to inspect the nuclear site at Parchin.

Iran, which is currently hosting a summit of non-aligned powers in Tehran, has produced 417 pounds of higher-grade enriched uranium since 2010, up from 145kg, the IAEA also said.

Under severe sanctions from the US and EU, Iran has repeatedly denied that it seeks to develop nuclear bombs.