Vienna - International Atomic Energy Agency (IAEA) inspectors were set to return from Iran to Vienna on Thursday, after visiting a new nuclear facility that was disclosed only last month, a diplomat close to the agency said.

The quartet of experts spent four days in the new uranium enrichment plant near Fordu, 100 kilometres south of Tehran, as well as in the capital itself, to verify that the underground site is not being constructed for military purposes.

The IAEA did not comment on the outcome of the inspection of the site, which is the second enrichment plant besides the one in Natanz.

According to the rules of the Vienna-based IAEA, Tehran should have informed about the new site as soon as it decided to build it, not years after construction began.

The revelation about Fordu again raised suspicions that Iran was trying to enrich uranium not to fuel civilian reactors, but to build nuclear weapons.

Experts and diplomats said before the inspector's trip that no technical equipment is likely to have been installed yet at Fordu.

The inspection was one of the agreed outcomes between Iran and world powers at talks in Geneva on October 1.

Iran's negotiating partners Britain, China, France, Germany, Russia and the United States are still waiting for Tehran to deliver its answer to a proposal to process Iran's nuclear fuel abroad as a confidence-building measure.

Iranian media reported that Iranian ambassador Ali Asghar Soltanieh would deliver the answer to the IAEA Thursday, though it would likely include changes to ElBaradei's proposal. (dpa)