DUBAI - Iran has sent a new batch of enriched uranium to fuel a medical research reactor in its capital, the country's nuclear chief said on Sunday, an indication Tehran is digging in as its standoff with world powers over the enrichment continues.

Fereydoon Abbasi-Davani, the head of Iran's Atomic Energy Organization, said a fourth batch of 20-percent enriched fuel produced inside Iran has now arrived at the Tehran Medical Research Reactor, according to the Mehr news agency.

Iran says the reactor produces medical isotopes used to treat cancer patients. Western powers believe Iran is stockpiling enriched uranium as potential fuel for nuclear weapons.

A third round of talks between Iran and six major world powers in Moscow ended last month without any agreement. United Nations Security Council resolutions require Iran to halt all enrichment of uranium, while Iran insists it has the right to some enrichment under the Nuclear Non-Proliferation Treaty.

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