Tehran: After more than four years, Iran has once again started enriching uranium at the Fordow nuclear site, a spokesman for the Atomic Energy Organisation of Iran says.

In doing so, Iran is violating a cornerstone of the landmark deal to prevent it from developing nuclear arsenal and placing pressure on the parties to the agreement to fulfil their commitments.

In this photo released by the Atomic Energy Organisation of Iran, spokesman Behrouz Kamalvandi briefs the media at the Fordow nuclear site near Qom, south of Tehran. Credit:AP

The Joint Comprehensive Plan of Action, as the deal is formally known, was struck between Tehran and world powers in 2015 but has been called into question since the United States pulled out of it unilaterally in May 2018 and revived sanctions on Iran that had been lifted under its terms.

Uranium gas was injected into the 1044 centrifuges at the Fordow facility earlier this week and uranium enrichment has now reached a level of 4.5 per cent, spokesman Behrouz Kamalvandi from the AEOI said.