Iran has not expanded its nuclear facilities in the last three months, a UN atomic watchdog report showed Thursday, in a possible confidence-building measure by Tehran before talks next week.

The International Atomic Energy Agency said that only four new uranium enrichment centrifuges were operating at Iran's Natanz plant and no additional machines at the Fordo facility.

It also said that Iran has also not begun operating any new-generation IR-2M centrifuges and that "no ... major components" had been installed at a reactor being built at Arak.

The faster IR-2M centrifuges are of concern to the international community because in theory they shorten the time needed by Iran to produce enough weapons-grade uranium for a nuclear bomb.

The reactor at Arak is a worry because it could provide Iran with plutonium, an alternative to uranium for a nuclear weapon, once it has been up and running for 12-18 months.

The quarterly IAEA report, the first since President Hassan Rouhani took office in August, was released ahead of a new round of talks between Iran and world powers in Geneva next week.

Three gruelling days of talks that involved US Secretary of State John Kerry and other foreign ministers ended with no agreement in the early hours of Sunday morning.

The United States, China, Russia, Britain, France and Germany (the P5+1) want Iran to scale back the most sensitive parts of its nuclear programme.

In return Iran wants UN and Western sanctions that have been causing the Islamic republic considerable economic problems eased soon, and its "right" to enrich uranium recognised.