Iran is prepared to modify its planned Arak heavy water reactor to help allay Western concerns, its nuclear energy chief said in published remarks that could be the first such suggestion by a senior Iranian official.

Western powers, preparing for negotiations with Iran on a long-term deal defining the scope of its disputed nuclear programme, fear Arak could provide a supply of plutonium - one of two materials, along with highly enriched uranium, that can be used for the core of a nuclear weapon - once operational.

The Islamic Republic has said the reactor is designed to produce isotopes for medical treatments, and has denied that any of its nuclear activity is geared to developing a bomb.

In an interview with Iran's state-run Press TV, Ali Akbar Salehi, head of the Atomic Energy Organisation of Iran, did not spell out how any changes could be made to the Arak plant.

Press TV reported Salehi as saying he did not believe Western concerns over Arak were genuine, calling them a "fabricated fire" used to put Iran under political pressure.

But he added: "We can do some design change, in other words make some change in the design, in order to produce less plutonium in this reactor, and in this way allay the worries and mitigate the concerns."

Heavy water reactors, fuelled by natural uranium, are seen as especially suitable for yielding plutonium. To do so, however, a nuclear reprocessing plant would also be needed to extract the plutonium.

Iran is not known to have any such reprocessing facility.

The fate of Arak was a big sticking point in talks last year that led to a landmark agreement to curb Iran's nuclear programme in exchange for some easing of sanctions.

Under the November 24 agreement Iran pledged to not install any additional reactor components or produce fuel for the plant during the six-month period of the deal.

US officials have made clear the reactor must be dealt with under any final settlement.

"They do not need a heavy-water reactor at Arak in order to have a peaceful nuclear programme," Wendy Sherman, the US Undersecretary of State for Political Affairs, told lawmakers in Washington on Tuesday.

Iran already has built a heavy-water production plant that is to be linked to the still unfinished reactor.

The future of the Arak site is expected to be one of the most thorny issues to resolve in the negotiations on a long-term nuclear deal with Iran due to begin on February 18.

Some Western experts have suggested a possible way forward might be to reconfigure the heavy water reactor into a light water reactor, which experts say would be much less amenable to any attempt at nuclear proliferation. - Reuters