The United Nations nuclear watchdog said Tuesday in a recently issued report that Tehran is preparing to use advanced IR-6 centrifuges at its underground Fordow site.

In its report, the International Atomic Energy Agency (IAEA) claimed that "Iran is escalating its uranium enrichment further by preparing to use advanced IR-6 centrifuges at its underground Fordow site that can more easily switch between enrichment levels."

Reuters cited the IAEA as saying that Iran informed it on Monday that passivation of the cascade - a process that precedes enrichment and involves feeding UF6 (Uranium Hexafluoride) into the machines - had begun on Sunday.

The new IAEA report claimed that Tehran has not informed the UN nuclear watchdog what purity the cascade will enrich after passivation.

However, Iran had previously informed the IAEA that the two IR-6 cascades could be used to enrich to 5% or 20% purity.

"The Agency has yet to receive clarification from Iran as to which mode of production it intends to implement for the aforementioned cascade, following the completion of passivation," the IAEA report indicated.

This comes after the IAEA's Board of Governors adopted on June 8 a draft resolution submitted by the US, France, UK, and Germany, criticizing Iran for what they claim were incomplete answers provided to the IAEA on uranium traces at "undeclared sites".

These claims were quickly refuted by the Head of the Atomic Energy Organization of Iran (AEOI), Mohammad Eslami, who said that Iran has neither secret or unwritten nuclear activities nor unreported nuclear sites.

Iran ceases all commitments beyond nuclear safeguard accords

In the same context, Iran has abandoned all commitments beyond the Safeguards Agreement in response to the International Atomic Energy Agency's Board of Governors' adoption of an anti-Iran resolution, an Iranian lawmaker said on Saturday.

Iranian MP and member of the Parliament's National Security and Foreign Security and Foreign Policy Commission Abolfazl Amoee condemned the resolution passed by the UN nuclear watchdog.

Iran's delegate to the IAEA had also denounced the decision the agency's Board of Governors took, which was the adoption of a resolution drafted by the United States and the E3. The decision came despite Russia's representative to the IAEA warning that such a decision would push success out of reach in the Vienna talks.

Before the release of the IAEA report that later led to the US and E3 submitting the draft, IAEA head Rafael Grossi visited "Israel", which raised questions regarding the nature of the visit ahead of the Body of Governors meeting and led to suspicions regarding the IAEA's impartiality.

Warning that if the IAEA continues to embark on the same path of issuing politically-motivated reports against Iran, Tehran would be required to respond via "proportionally harsher" actions.