Iran on Sunday notified the International Atomic Energy Agency that it would apply a protocol granting inspectors greater access to its nuclear sites, a further step in the implementation of a historic deal struck with world powers, the UN nuclear watchdog said.

The announcement came as the European Union's foreign policy chief Federica Mogherini and  Iranian Foreign Minister Mohammad Javad Zarif were set to make a statement on the lifting of crippling sanctions on Tehran, as part of the so-called Joint Comprehensive Plan of Action signed in Vienna in July.

"On October 18, the director general of the International Atomic Energy Agency was informed by the Islamic Republic of Iran that... Iran will provisionally apply the  Additional Protocol to its Safeguards Agreement, pending its ratification by the  (parliament)," the IAEA said in a statement.

The additional protocol is a voluntary agreement enabling the IAEA to gain greater access to Iran's nuclear facilities and research, to ensure that no atomic material is diverted to any covert weapons programme -- an aim denied strenuously by Tehran.

Iran had been a signatory to the protocol from 2003 until 2006 before pulling out of the agreement.

Under the landmark deal struck in July, Iran pledged to dramatically scale down its nuclear activities in order to render any effort to make an atomic bomb virtually impossible.

In return, the world powers must finalise the mechanism for lifting UN and Western sanctions.

The EU was due to formally announce the lifting of its punitive measures on Sunday, although this is not expected to take effect before December.

On Thursday, the IAEA said it had completed on schedule gathering information in its probe into Iran's alleged past efforts to develop nuclear weapons.

The agency's chief Yukiya Amano is expected to provide a final assessment on the investigation by December 15.