Atomic Energy Organization of Iran's joint press conference in Tehran. (AFP)

The UN's nuclear watchdog confirmed Monday that Iran was installing advanced centrifuges as the troubled 2015 deal with world powers over Tehran's nuclear programme threatens to fall apart.

The International Atomic Energy Agency (IAEA) said in a statement that on September 7 it had "verified that the following centrifuges were either installed or being installed...: 22 IR-4, one IR-5, 30 IR-6 and three IR-6s".

The IAEA's confirmation comes a day after Tehran hit out at European powers, saying they had left Iran little option but to scale back its commitments under the 2015 Joint Comprehensive Plan of Action (JCPOA).

The IAEA added in its statement that the centrifuges had been installed at Iran's Natanz facility and said "all of the installed centrifuges had been prepared for testing with UF6 (uranium hexafluoride), although none of them were being tested with UF6 on 7 and 8 September 2019."

"In addition, in a letter to the Agency dated 8 September, Iran informed the Agency that it would reinstall the piping at two R&D lines to accommodate a cascade of 164 IR-4 centrifuges and a cascade of 164 IR-2m centrifuges," the agency's statement said.